On Broadway: put a line of tap dancers on stage, and the show stops--guaranteed.

Throughout most of the 1920s, '30s and and '40s, tap ruled Broadway musicals. It was the dance vernacular, a home-grown popular entertainment that had sprung from the uniquely American intersection of African and Irish dance forms. With its upbeat rhythms, relaxed posture and freewheeling energy, tap seemed to breathe the air of democracy--especially once it migrated from the country's theater stages to its even more popular movie screens.

But when the forces unleashed by Agnes de Mille and Jerome Robbins transformed the dance element in musical theater from a pleasant diversion to an integral part of the plot, tap dancers suddenly became scarce on Broadway. History had decreed that the dancing now had to be related to a musical's characters, and Puerto Rican street kids and Austrian nuns would hardly be credible doing time slops. Dream ballets and integrated dance numbers replaced flashy kick lines, and for a while, it looked as if tap would go the way of the cakewalk and the waltz, pretty, much disappearing from our musical theater.

It didn't happen, as anyone who's up on Broadway's current musicals can tell you. Sure, there are the pointe-shoe pretensions of Phantom of the Opera, the sexy slitehrings of Chicago, and the disco moves of Mamma Mia! But tap numbers are not exactly bard to find on Broadway these days. They dominate the choreography of 42nd Street and Thoroughly Modern Millie, and they're important elements in The Producers, Gypsy and The Boy From Oz. Most of the choreography in Hairspray is based on teen dance fads of the '60s; but everyone's favorite number, "Timeless to Me," is a classic soft shoe duet. There are allusions to tap even in Twyla Tharp's Movin' Out, in the Army drill segment and in the horseplay choreography for the three guys at the center of the story. And let's not forget Stomp, fine long-running off-Broadway phenomenon that may not resemble classical lap dancing, but surely comes out of the tap tradition.

Tap numbers started coming back to Broadway around the time producers began to realize that Jerome Robbins really, really wouldn't be doing any more new shows, that Bob Fosse could do only one musical a year, and that the artistic strides being made in the musical theater form didn't necessarily generate profits for investors. The search for new hits led directly to old hits, and No, No, Nanette proved that 1971 audiences were no more sophisticated than those of 1925, when this confectionery trifle first became a hit. (Don't get me wrong--who can blame audiences for loving a show with "Tea for Two" and "I Want to Be Happy" in the score?) Tap was suddenly back, in a slew of nostalgic offerings--Irene, Sugar Babies, Anything Goes, Me (and My Girl, and 42nd Street (in its first incarnation). In 1967, the all-black, Pearl Bailey edition of Hello, Dolly! had shown. Broadway that black stars would draw black audiences, and subsequent shows like Eubie! (with Gregory and Mare ice Hines) and Bubbling Brown Sugar solidified the lap revival. In 1978, even Harold Prince, an architect of the "concept" musicals that had helped eclipse lap on Broadway, climbed on the bandwagon and included a quartet of tapping porters in On the Twentieth Century. Gregory Hines returned in Sophisticated Ladies in 1981, Tommy Tune tapped alongside Honi Coles in My One and Only in 1983; and that same year, The Tap Dance Kid introduced a young dancer named Savior Glover.

In some ways, of course, the return of tap signaled a kind of exhaustion in the choreographic impulse on Broadway. But it also betokened a renewed recognition that this abiding art form quite simply galvanizes audiences. Ask the millions who love Riverdance--a geometrically arranged array of bodies combined with the percussive thunder of many feet striking the floor seems to be a surefire formula for stopping a show. While Jerry Mitchell's Hairspray soft-shoe stops the show with only two performers, he understands the power of amplification. "If you see one character tapping, it's exciting," he says. "If you see two characters do it next to each other, it's thrilling. But when you see a stage frail of dancers do fire exact same thing on the same beats with the exact same accents, it explodes. It carries over the footlights in waves of. explosions. It always works."

Even toddlers get it; a friend with a four-year-old reports that her daughter always gets rap to join in when Marvin, PBS's tap-dancing cartoon horse;, brings down the house in his big, Broadway-style production number. The precision tap dancing of the Rockettes, the chorus kids in 42nd Street, the flappers in Thoroughly Modern Millie, have exactly the same, universal appeal.

Playwright and dance fan Wendy Wasserstein has written lovingly of her girlhood years at The June Taylor School of the Dance in Manhattan. "I would mark time during ballet, jazz, and acrobatics and wait for tap," she says. "It seemed integrally related to the rhythm and heat of the music, as opposed to just being about the state of my metatarsal arches." And, that, perhaps, is the ultimate secret of the happy and presumably never-ending marriage between tap dancing and Broadway musicals: invariably, tappers look like they're having a good time. For an audience, nothing is more infectious.

Sylviane Gold has written about theater [or The Wall Street Journal, Newsday, and The New York Times.