Pete Seeger may well be the best choir director in the world. At the Merriweather Post Pavilion Friday night, the 71-year-old Seeger had the large crowd (many of whom had come merely to hear Arlo Guthrie perform "City of New Orleans" and "Alice's Restaurant") singing three-part harmonies on the old church hymn "Old Hundred." With his nonchalant, avuncular manner, Seeger made singing along seem the most natural thing in the world. "There's no such thing as a wrong note," he explained, "as long as you're singing." Before the evening was over, Seeger even led the crowd in a whistle-along.

The 43-year-old Guthrie didn't sing either of his big hits, but he did sing two of the best songs ("Tom Joad" and "I Ain't Got No Home") by his dad -- and Seeger's old music partner -- Woody Guthrie. The younger Guthrie suddenly stopped singing in the middle of "Garden Song" and extrapolated the line about the crow into an impromptu, rambling comic monologue that touched on monster movies, album stickering and the folk process. He also picked out a lively blues guitar solo on Big Bill Broonzy's "Key to the Highway."

Buskin & Batteau, the folk duo that opened the show, look disconcertingly like a piano-playing Noel Paul Stookey and a fiddle-playing Billy Joel, respectively. Backed by bassist Paul Guzone and percussionist Marshall Rosenberg, David Buskin and Robin Batteau played their original folk-cabaret tunes, both comic and sentimental. They played a brisk medley of the famous commercials they've written -- everything from "All Aboard Amtrak" to "The Heartbeat of America." They then immediately poked fun at themselves with a funny number about meeting with an ad agency that explained, "We Want Our Condoms in Your Jingle."