"Luther, he doesn't know when to quit," said J.B. Christensen of Martinsburg, W.Va., who helps organize the Blue Heron Blues Fest. "From what I've heard, he wants to play all night. It doesn't get any better than this."
In the style of his mentor Muddy Waters, Allison let his band warm up the crowd before he walked on stage and started talking to the audience with his guitar.
"Can I get a witness?" he sang. And the crowd roared.
Wearing a sky blue shirt with a guitar to match, Allison was expected to play until at least 11 p.m.
Fans speculated whether he would go to Oliver's Pub, a Hagerstown blues club, after the show.
Kevin Boyle, 34, of Frostburg, Md., was hoping to interview Allison.
"He's been a hero of mine for a long time. His music is just intense," said Boyle, who hosts a weekly blues show on WFWM, Frostburg State University's radio station.
Amy Culler, 23, of Frederick, Md., said she recently started listening to the blues after her mother bought some music by blues legend Robert Johnson.
Even before Allison's show started, Culler had compiled a list of compact discs she wants to buy from the bands performing downtown Saturday afternoon.
Jim Sellgren, who lives in the Hagerstown area, brought his whole family to the show, including his mother, Josephine, who was visiting from Detroit, and his two children.
"I thought it was too loud," said his son Cory Sellgren, 9, who normally listens to Amy Grant. "My mom brought cotton and I put it in my ears."
A former Pittsburgher who know lives in Martinsburg, W.Va., said he was impressed with Hagerstown's blues festival.
"The blues down here beats everything I've heard in Pittsburgh," said John Bocan.
Joe Musti, 43, and Kristi Walsh, 36, of York, Pa., have listened to Allison many times, but Saturday was their first time to hear him play live.
"He think's he's the greatest thing since sliced bread," Walsh said.
The couple, who read about the blues festival in a blues magazine, ate at nearby Twilights Ristorante before going to the main event at The Maryland Theatre.
"I got excited over dinner and he got excited over the blues," she joked.
Before Allison, solo guitarist Kelly Joe Phelps primed the crowd with his doleful lap-style slide guitar playing.
Bantering with the audience, Phelps said he likes being a traveling musician because he gets to meet so many nice people.
"We love you, baby," an audience member called back.