NEW YORK >> In the end, the theater was shuttered as it lived: mercifully dark, faintly smelling of body fluids and crammed to capacity with a mixture of starry-eyed young actors and ardent comedy pilgrims, each hoping for an intersection with comic history on an otherwise unremarkable corner of 26th Street.

The line between performer and audience member at the Upright Citizens Brigade Theater in Chelsea — New York’s high temple of improv comedy — was finally obliterated around 1:30 Wednesday morning, as seats were vacated and the crowd streamed onto the stage like NBA fans after a championship.

It was the last hurrah at the group’s longest-standing and most storied location, the basement beneath a Gristedes supermarket, which has been its flagship since 2003 (after a stretch in a former strip club). The basement space, soon to be replaced by a new location on 42nd Street, was closely identified with the rotating cast of rising stars who performed there; it was a dank but beloved cradle to household names like Amy Poehler, Aziz Ansari and Kate McKinnon in the unpolished early phases of their careers.

Shannon O’Neill, artistic director of UCB’s New York operation, said in an interview Tuesday that the building’s rough edges became embedded in the group’s DNA.

“It has all of these flaws that we just kind of embraced,” she said, like hissing noises and curious drips from exposed pipes above the stage. “It puts a little more hustle in the bones.”

Some of the theater’s quirks, including a steep staircase at the front entrance, made it prohibitive for fans in wheelchairs or with other mobility constraints. A major impetus for the move is to bring the organization into compliance with the Americans With Disabilities Act.

But the transition, from the literal underground to the former home of the Pearl Theater Company in Hell’s Kitchen, a short walk from Broadway, also carries unavoidable symbolic weight.

When it arrived in New York in 1999, Upright Citizens Brigade was a well-regarded but minor player in a comedy scene dominated by stand-up giants like Chris Rock and Sarah Silverman. Today, UCB is a growing and influential empire, with four locations, including two in Los Angeles and one in the East Village; a reliable pipeline to “Saturday Night Live”; and a lucrative business selling improv classes and workshops to aspiring actors and corporate clients like PwC.

But if UCB’s organizers plan to clean up their act as the business expands and the theater moves uptown, they showed no evidence of that Tuesday.

Over the course of a show that lasted more than five hours, house actors and their confederates in the crowd giddily flailed toward — and occasionally touched — the sublime, partaking in a drama-school-worthy bacchanal complete with tribal chanting, ritual sacrifice and a dance-off to Sisqo’s “Thong Song.”

The show, conceived by O’Neill, consisted of back-to-back performances from six “Harold” teams, the company’s name for specialists in a kind of long-form improv based on rapid-fire, loosely interrelated sketches. An early skit involved a family at a funeral home whacking the swollen corpse of its patriarch with a Wiffle bat. The scenarios became more gleefully deranged from there.

Backstage beforehand, performers, many of whom had spent years in the improv trenches together, exchanged hugs and compared photos of the admission line that wrapped around Gristedes and an adjacent McDonald’s — the theater’s longtime unofficial cafeteria. In a narrow, fluorescently lit hallway papered with old show flyers, they fueled themselves with beer, coffee and Red Bull while psyching each other up for the “last dance” and speculating about the future.

“You’ve got to step up the way you dress! Articulate!” Alexis Pereira, a member of the house team Some Kid, joked with his teammate Andy Bustillos. Pereira had tapped into a current of anxiety that was coursing through the room. How much would moving to 42nd Street change UCB? Would anything ever be as fun as the basement?

“It’s always felt a little punk rock to me,” said Bustillos, who began taking classes at Upright Citizens Brigade in 2010. “When I first came here, I used to be in hard-core bands and I thought, ‘Oh this is cool: You go in a basement and it’s dark and it smells and the beer is cheap.’ I loved that about it.”

Jesse Lee, who took his first class in 2006, said he expected the new theater’s proximity to the theater district to attract a different kind of audience. “This place is kind of nondescript; it feels kind of like a secret,” he said. Lee said he would miss the clubhouse atmosphere of the basement but, in true improv fashion, was staying open to the possibilities of a new incarnation. “What’s exciting is that you never know where UCB will go from here,” he said.

Onstage, after all six Harold teams had performed, the show became a kind of delirious free-for-all, with O’Neill issuing a series of outlandish prompts and audience members, many of whom seemed to have been waiting for this moment, joining the fray. One game, which involved eating raw jalapeños and chugging from a half-gallon of milk, ended in several performers’ vomiting into a trash barrel onstage.

Then there was an impromptu, all-female dance party and the “Thong Song.” Seats emptied and the dance-off began. O’Neill, who has been with UCB since 2000, decreed, for some reason, that anyone who lost a dance battle had to be sacrificed to the dumpster in front of the theater. The crowd didn’t miss a beat, and losers were hoisted in the air — crowd-surfing-style — and carried out.

When enough of them had met this fate, they turned the dumpster into a makeshift second stage and started playing improv games of their own among the trash.

It would have been almost too perfect an argument for the group’s resilience if they had planned it. But if anyone saw it that way, no one said anything — they were just making things up as they went along.

© 2017 The New York Times Company