For Ellen and Irene Kossoy, the phrase "identical twins" is no exaggeration. They wear their hair the same, wear identical glasses, have the same big, Kennedy-esque smiles, and their speaking voices are hard to distinguish. They even live on opposite sides of a twin house in the Boston suburb of Somerville, Mass.

And even while sitting across a table from them at a Harvard Square coffee shop, it's difficult to keep track of which one is which.

Until "O Brother, Where Art Thou?" came out two years ago with their version of "I'll Fly Away," most music fans didn't keep track of either one.

It's been a long time between albums for the Kossoy Sisters; nearly a half-century, in fact, since the 1956 release of "Bowling Green," their only other release to date (although Irene also recorded an album with ex-husband Tony Saletan in the late '60s).

Recorded when the sisters were only 17, "Bowling Green" has rarely, if ever been out of print since its original release on Tradition Records, and it's easy to understand why.

The sisters' singing is perhaps best described as "haunting," with Irene handling most of the lead vocals and Ellen nailing impossibly high harmonies with apparent ease, accompanied by the spare instrumentation of their own guitars and guitarist/banjo player Erik Darling.

It's a pleasant surprise to discover that "Hop On Pretty Girls" - released in November on the Living Folk label - sounds pretty much how one would expect a Kossoy Sisters album to sound in 2003.

The instrumentation is a bit more varied than on the first album, and a couple of original numbers have made the cut this time around (as well as a re-recording of the first album's "The Wagoner's Lad"), but the sisters' vocals happily show little evidence of the passing years. The singing is clearly the work of individuals who are older than those who made the first album, but any fan of "Bowling Green" will immediately recognize the voices.

So why did it take 46 years to make a second album?

According to Ellen, "Part of it is inertia. Part of it is the fact that we lived over a thousand miles from each other up until almost four years ago. We'd get together maybe once or twice a year and play music, but most of the time we were apart, so it just didn't seem like an opportune time to do it."

Born in New York City in 1938, the Kossoys were exposed to music at an early age.

"We always sang together," says Irene. "Ever since we were able to talk, we were singing. Our mother's sister lived with us and the two of them were always singing together in harmony, so we kind of figured that out fairly quickly when we were about six or so. We started singing these songs when we were around 15. We liked The Weavers -- they were popular -- and with our older sister we used to go to what were then called hootenannies, which were different from hootenannies in the '60s. They were more political, not as mainstream."

"We went to a summer camp when we were 15, and it was right near where Pete Seeger lived. So he would come down and bring people with him. So we just started getting interested in playing the guitar. Then we started going to Washington Square in the Village every Sunday, just hanging out and learning songs."

The Greenwich Village of the '50s and early '60s was a hotbed of writers, musicians and leftist political discourse, and the sisters met dozens of artists who were either already big names in folk music or soon would be: Dave Van Ronk, Ralph Rinzler, Mike Seeger, John Cohen and Mary Travers among them.

One of the musicians they had met during this period was Darling, who in 1958 would replace Pete Seeger in The Weavers and in 1962 scored a substantial hit as a member of the Rooftop Singers with "Walk Right In." In 1956, however, Darling was the sisters' occasional live accompanist and is the only other musician heard on "Bowling Green."

"We were hanging around Washington Square, and a woman named Lucia Walker came over to us and asked us if we would like to do some concerts," Irene says. "After the off-Broadway theatres would go dark, they would have midnight concerts. So we started doing a number of these concerts, some with Erik Darling. So then Paddy Clancy of the Clancy Brothers was starting up Tradition Records and he approached us and asked if we would do a record."

"We recorded a whole lot of stuff, and they picked which ones they liked," says Ellen. "I remember that there were some we sang that they didn't put on there."

"I think it did well," says Ellen. "Times were different then. There wasn't as much out there as there is now. It's never really been out of print. It would come back into print, or people would find it in used (record) stores. Financially, it didn't do that well for us, but it sold a lot of copies, and a lot of people knew of it."

It was also during this period that the sisters got to know Woody Guthrie, whose "Belle Starr" is covered on the new album. Though ill with Huntington's Chorea and retired from performing, Guthrie at this time was still capable of leaving the hospital for short periods of time and first met the Kossoys when they performed at a concert of his songs.

"He was in a hospital in Morristown, N.J., and we would go with Ralph Rinzler to visit him," says Ellen. "Sometimes we'd just stay in the hospital and visit him, and sometimes we'd take him out and either go to somebody's house or to Washington Square."

"He was somewhat mobile; he could walk, but he was staggering. His mind was still okay, but he didn't talk a whole lot, and his speech was slurred, so he gave the impression of being drunk. It was a real problem in Washington Square where we had to keep pulling him out of the hands of policemen. He had trouble playing instruments, but he still loved to listen, and he was still very funny."

The highwater mark of the Kossoys' career can perhaps be regarded as their appearance at the 1959 Newport Folk Festival on a program which also featured Pete Seeger, the New Lost City Ramblers, the Stanley Brothers, Earl Scruggs, Odetta, the Clancy Brothers and the Kingston Trio.

No additional records were forthcoming, and after college each sister married and settled in a different part of the country, with further live appearances coming only infrequently in the coming decades.

Asked why the act drifted apart, Ellen says, "Well, we started college, and then almost immediately afterwards, I got married and moved to St. Louis. We just started different lives. I think also the hootenanny thing was coming into popularity at that time."

Wouldn't that have just been all the more reason to stay together and cash in?

"Well, except that we would have been expected to wear these frilly dresses with petticoats, which just wasn't our style at all," says Irene. "And Ellen was still singing with other groups around St. Louis, and I was singing with my husband, and he and I were getting a lot of gigs."

"We were still doing occasional things, like Fox Holler Festival, and we did one tour of California in the early '80s. We would do coffeehouse things around St. Louis when I came to visit, or when Ellen came here, we would do some things."

The Kossoys' public awareness skyrocketed two years ago with the release of the Coen Brothers' movie "O Brother, Where Art Thou," in which the sisters' 1956 recording of "I'll Fly Away" was used.

And though a re-recorded version by Allison Krauss and Gillian Welch ended up on the soundtrack album, the song's presence in the movie gave the sisters a visibility they hadn't seen in years.

"Since 'O Brother' came out, people are rediscovering us," says Ellen. "Up until the last year or two, when we gave a concert it was always older people that would show up for it. And now a lot of young people are showing up, and it's just great to see it."

Interestingly, the song's inclusion in the movie came as a total surprise to both sisters.

"I was visiting my son in California two Christmases ago, says Ellen. "And we decided to go to the movies one afternoon. 'O Brother' had just opened out there -- it hadn't opened here yet -- and since we both liked Coen Brothers movies, we decided to go and see it. So we were just sitting there, and all of a sudden I heard Irene and me singing in the movie."

"It was all negotiated through Rykodisc, so we didn't even know," says Irene.

Have the sisters seen any money from the movie?

"A little bit," says Ellen. "Not a whole lot. Our contract with Rykodisc is based on the contract that we had with Tradition Records when we were 17 years old."

According to Ellen, the use of two different versions of "I'll Fly Away" is still a bit of a mystery.

"As far as we know, (Krauss' and Welch's version of 'I'll Fly Away ') had been recorded before they put the movie out and using us in the movie was a later decision. The CD had already been made, and (for the movie) they were going back and forth between our version and the other. We think it's (director/writer) Ethan Coen who made the decision to use us, but we're not absolutely sure about that."

The decision to start working together again was made a couple of years before the release of "O Brother, Where Art Thou?"

"We had pretty much decided that we wanted to get together and start singing again when Rykodisc reissued our CD (in 1997)," says Ellen. "At that point, I was still living in St. Louis, but the kids were grown and gone, my husband was gone, and I had just retired from my job, so at that point I really didn't have anything tying me to St. Louis. Irene said, 'Why don't you move here?'"

"Hop On Pretty Girls" is the first release by the recently revived Living Folk label, which released a number of folk albums in the '70s.

"(Living Folk label owner) Peter Johnson was kind of out of things for a while, and now he's back into it, and we're the first CD he's put out."

According to Irene, "The songs we selected mostly are traditional songs. That's what we do and that's what we love most. We worked with Pete Sutherland, who's a phenomenal musician who lives in Vermont. It was just songs that we liked and wanted to do. It was a lot of fun doing the recording. A lot of people think of it as work, but we just had a good time."

When asked if it'll be another 46 years until the next record, Ellen laughs and says, "I don't think we'll live that long."

"When I'm a hundred years old, I don't think I'll still be able to sing," adds Irene. "You never know how many people you're influencing. We got an e-mail from Ethan Coen, who really put it well. He said that making a movie is like putting a note in a bottle and throwing it out in the ocean. You just never know who's going to pick it up and be influenced by it."

Finally, the question has to be asked: So which one is the evil twin?

Laughing, both sisters reply, "We both are."