CHICAGO - On a blustery fall afternoon, Andy St. Clair slips into an empty club, with rows of tables, wooden chairs, and a bare stage awaiting its next bit of comedy magic.

It doesn't look like much, but the stage is something of a shrine.

This is the Second City, the place where legions of comics - among them Tina Fey, Stephen Colbert, Steve Carell, Mike Myers, Chris Farley, John Belushi, Bill Murray and John Candy - sometimes killed, sometimes flopped, but always tried to make 'em laugh.

This weekend, the theater marks its 50th anniversary, a milestone that's even more impressive in the ephemeral world of show business. Second City has survived and thrived for a half-century with the same formula: small, youngish casts; parody, satire, and improvisation; and hip, irreverent, topical, often political humor.

Decades ago, it was Alan Arkin in a rain hat and slicker phoning God - "That's N-O-A-H," he tells the divine - and auditioning ark candidates. Thirty years later, it was Carell (Arkin's cast mate in Little Miss Sunshine) as a job applicant ordered to stomp his foot and disguise his voice so a blindfolded personnel manager could guard against biases.

From one generation to the next, Second City has cranked out talent with clockwork regularity. "It's a comedy factory," says Harold Ramis, a former cast member turned director-writer-actor-producer.

Now it's Andy St. Clair's turn. He's at the Wells Street theater this day for rehearsals for the 97th main stage show, The Taming of the Flu.

Tall with a Midwestern geniality, St. Clair, 34, made it to the main stage after working his way up the ranks over six years, much like a rookie moving from the minors to a championship team. So his description of Second City is apt.

"I call it the comedy Yankees," he says with an easy grin. "When it's not funny, people are going to be, 'What's wrong with the Yankees?' But when it is funny, they're going to be, 'Well, they're supposed to be funny. They're the Yankees.' "

The origins of Second City read almost like a TV pilot: A group of intellectuals, mostly from the University of Chicago, forms a comedy theater in a run-down former Chinese laundry at the end of the buttoned-down 1950s.

And then . . .

Cue the laughter, right? In this case, yes, this was the start of a 50-year-plus run for a troupe that took its name from a snobby reference to Chicago in an A.J. Liebling piece in the New Yorker. Some early cast members were recruited from the group's predecessor, the Compass Players, which featured Mike Nichols and Elaine May, known for their legendary comedy skits that helped establish improvisation.

So what's the key to longevity for a theater that has mushroomed into a $30 million annual business with two locations (Chicago and Toronto), four touring companies, three training centers, and alumni that have made a splash on Saturday Night Live, The Office, 30 Rock, movies and more - in front of and behind the cameras?

The explanation sounds deceptively simple.

"The reason it's successful is because we stay relevant," says Andrew Alexander, cochairman and chief executive officer since 1985.

The revue titles bear that out. Among some recent ones: Between Barack and a Hard Place (the president and first lady both saw the show); No Country for Old White Men; Iraqtile Dysfunction.

The Second City stage is a taboo-free zone, mining humor from Guantanamo and torture, 9/11 and terrorism, and less timely but equally grim subjects such as assassination and death.

Consider a classic skit, "Funeral," written in the 1960s and still performed on tour. Mourners gather for a funeral and slowly learn from the somber widow how the deceased met his untimely death: His head got stuck in a gallon can of beans.

"The best comedy touches something that's timeless and universal in people," Ramis says. "When you hit it right, those things last."

Pushing the envelope is part of Second City tradition. Just ask Sheldon Patinkin, who has been with the show all 50 years and is now artistic consultant.

He remembers one skit where robbery victims are waiting for Superman, and when he arrives, he's in a wheelchair - shades of Christopher Reeve. "There was shocked silence," Patinkin says, "then enormous laughter."

Second City humor isn't designed to shock, just to be funny. Skits deal with the fodder of everyday life - marriage, money troubles, neighbors, bosses.

These days, there are more sports and pop culture references, though there is still a heavy emphasis on Chicago, whether it's the hapless Cubs or the city's checkered political reputation.

Second City exploded on the national scene in the 1970s with the popularity of Animal House and Saturday Night Live - both featuring Belushi. The troupe's Chicago and Toronto casts became a comedy college for future SNL casts.

Early on, it was Gilda Radner, Dan Aykroyd, and Bill Murray. Then Mary Gross, Tim Kazurinsky, Jim Belushi, Mike Myers, Chris Farley, and Tim Meadows. Then Rachel Dratch, Tina Fey, Jason Sudeikis, and Horatio Sanz, among others.

Second City has always been ensemble comedy.

Over the years, the cast has played before its share of celebrities. Among them: Sir Edmund Hillary, the Mount Everest hero, who came with a Sherpa to watch a mountain-climbing skit; Cary Grant; and Groucho Marx. Ramis says the sharp-tonged comedian teased him about the size of his hair and nose, asking if they were fake. They weren't.

But this is a show for the masses, and it's the audience that suggests topics for improvisation, and gives thumbs up or down.

"I was booed off the stage - that was not fun," says George Wendt (Cheers), a cast member in the '70s, recalling a "poor taste" improvisation about nuns, priests, and sex. Wendt walked outside, before being called back.

After working with scores of aspiring comic actors, CEO Alexander says there's no way to "teach somebody to be funny." But Second City can build confidence; the cast does eight shows a week.

Like any business, not every part succeeds. Second City stages opened and closed in cities including Detroit, Cleveland, Santa Monica, Calif., New York, and Las Vegas. In Vegas, Patinkin notes, "one subject couldn't get laughs - gambling."

And not every Second City performer ends up in the entertainment business. Many have become homemakers, doctors, lawyers, even cops.

Second City is celebrating its 50th anniversary with reunions, panels, and shows.

And then?

"I don't see any reason why it shouldn't go on," Patinkin says. "Satire is always relevant."

So mark 2059 on the calendar.

Maybe someone will be on the Wells Street stage, joking about a guy who died when his head got stuck in a can of beans.