Woodstock -- An hour after Elvis Costello and Levon Helm strapped on their acoustic guitars, Helm leans into the microphone and says: "Let Elvis do one."

So Costello, who had been content to play acoustic guitar and sing backup with the former Band drummer and singer, steps up to the mic. In a voice as meaty as a thick sirloin steak and as sharp as a knife, Costello wails: "You better help me baby/I can't do it by myself."

As he stretches "help" into a six syllable plea that ricochets off the bluestone walls of Helm's home studio, you can almost see the goose bumps popping on 150 stunned fans.

This was Saturday night at one of Helm's Midnight Rambles, where Costello was the surprise guest. This was two of the greatest voices in rock 'n' roll making music for the sake of music. This was music that was as down home as the Ramble's homemade brownies (with Helm's name on the icing) and hot popcorn.

This was Costello driving up from the city and down Helm's dirt road for one of the jams that have featured guests like Dr. John, Donald Fagen and Emmylou Harris. In a midnight blue suit with a matching shirt and tie, Costello walked out on the floor-level stage like he was one of the guys. No announcement. No spotlight. Just a slight smile, a little wave and an "all right, we're gonna try one for ya right now" from Helm, his voice strong, but still a bit frayed from his bout with throat cancer.

This was unrehearsed music -- "wrong key,'' Helm said after a false start on "Man of Constant Sorrow," the fourth song of the set and the first with Costello singing fervent harmonies to Helm's fertile lead.

Costello would smile after he helped sing the first chorus of "Atlantic City:" "Everything dies/Baby that's a fact/But maybe everything that dies/Someday will come back." He would holler "Don't Ya Tell Henry." And he'd shout "ooh" as Port Jervis blues man Little Sammy Davis led Helm and the band in a "have some fun tonight" version of "Long Tall Sally."

But he waited an hour until he led the band. This wasn't a greatest-hits set. He introduced new tunes he just recorded with another surprise guest, New Orleans' pianist Allen Toussaint, who's produced singles like "Mother in Law," arranged horns for the Band and played the rippling roly-poly piano lines that, on Saturday night, glistened like his bright red shirt.

Toussaint and Costello teamed up on a mouth-dropping ballad with the lyric: "How long does a promise last/How long can a lie be told." Costello hushed the standing room only crowd with these words: "There must be something better than this/Because it can't get much worse/What do we have to do/To send a river in reverse."

And then, just after midnight, Elvis Costello and Levon Helm went back to having fun.

Helm shook a fist. Costello cracked a smile. And they invited their 150 new friends to join them with these words that, on this February night, didn't seem one bit corny: "Everybody just sing, sing, sing/Let's all begin to do our thing/And make a better world to live in."

Levon Helm gives Elvis Costello a hug after their performance together on Saturday February, 11.

Elvis Costello performs with the Levon Helm Band.

Sammy Davis performs with Elvis Costello and the Levon Helm Band.

Elvis Costello and Amy Helm perform with Levon Helm and the Levon Helm Band.

Elvis Costello and Amy Helm perform with Levon Helm.

Elvis Costello and Sammy Davis perform with the Levon Helm Band.

Elvis Costello and Amy Helm perform with the Levon Helm Band.

Levon Helm gives Elvis Costello a salute after their performance.

Levon Helm performs with Elvis Costello and the Levon Helm Band.

Elvis Costello and Sammy Davis perform with Levon Helm and the Levon Helm Band.

The hands of Allen Tousaint play the piano while performing with Elvis Costello and the Levon Helm Band.