NASHVILLE — Considered among the best to ever sing bluegrass, Ralph Stanley and Del McCoury traditionally headline their own shows. Teaming up Thursday in the Ryman Auditorium's bluegrass series, they drew 2,000 fans — about double what each drew on his own at separate shows there last summer.

The rising interest in bluegrass — fueled in part by McCoury's work with such bluegrass outsiders as Steve Earle and Phish and by Stanley's contributions to the million-selling "O Brother, Where Art Thou?" soundtrack — also helped swell the numbers.

Ralph Stanley II handled lead vocals early in the 21-song set by Stanley and the Clinch Mountain Boys. Then he yielded to his famous father, who sang lead, to rousing applause, on three songs from "O Brother": "Man of Constant Sorrow," the a cappella "Oh Death" and the gospel classic "Angel Band." Stanley first recorded the songs a half-century ago.

In his unworldly mountain tenor voice, he also performed the Carter Family-derived "Daddy's Wildwood Flower," the sacred "One Drop of Water," "Little Maggie" and "The Hills of Home," a tribute to his late brother, Carter.

The Del McCoury Band was joined midway through its opening set by former Clinch Mountain Boy Ricky Skaggs, who played mandolin and sang harmony on Cindy Walker's "The Bluegrass Country." The song appears on the McCoury band's new album, Del and the Boys, released Tuesday on Skaggs' Ceili Music label. Skaggs also bandied with McCoury on the instrumental "Bluegrass Breakdown."

McCoury is approaching his 10th anniversary with the same personnel: sons Ronnie (mandolin) and Rob (banjo), Jason Carter (fiddle) and Mike Bub (bass). The group's time together shows in its presentation, down to the dapper, coordinated suits the bandmembers wear.

Around a single microphone, McCoury sings in a high, lonesome voice, blending frequently with the others in tight vocal harmonies. Whether on breakneck instrumentals or slower story songs, the musicians play with great skill, appearing to interact telepathically.

Commendable, too, is the group's willingness to step outside the standard bluegrass repertoire. Among the 19 songs in its Ryman set, the McCoury band performed Richard Thompson's "1952 Vincent Black Lightning," the Lovin' Spoonful's "Nashville Cats" and Frank Sinatra's "Learnin' the Blues."

But the group drew inspiration most often from Bill Monroe — the late "Father of Bluegrass" and McCoury's former employer — on numbers such as "Get Down on Your Knees and Pray," "Body and Soul" and "Rawhide."