Madness is nothing new to rock & roll. But the rambunctious antics of a 12-year-old are another matter, which might explain this Tarzan yell from Zac Hanson, the cherubic, gap-toothed drummer for the pop trio Hanson. A moment ago he bolted from a Hollywood photo session to swing from a convenient rope. And now he's running repeatedly, happily and headfirst into a closet door, laughing with sheer delight. Cut the boy some slack. This has been a long, remarkable year for Zac and his two big brothers, Taylor, 14, and Isaac, 17. First, the flaxen-haired band out of Tulsa, Oklahoma, scored a No. 1 single with the infectious ear candy of "MMMBop." Hanson then sold more than 5 million copies of their Middle of Nowhere album in the U.S. alone. Now the trio is up for three awards at this week's Grammys in New York, competing against the likes of Puff Daddy and the mighty Rolling Stones. "We kind of ended 1997 with a bang," says keyboard player Taylor. "We did all kinds of stuff: David Letterman, Saturday Night Live. Some days we were on three different stations in one day. After that we said let's take a break."

That meant a few weeks back home, but even there they couldn't escape the notoriety that comes from constant airplay on radio and MTV, or from teen magazines obsessed with their every move. The garbage collector congratulated the boys on the birth of a new baby sister, Zoe (making the Hanson brood now a total of seven brothers and sisters). you could say that their lives have changed.

"What is really crazy is, people drive across the country 10 hours to just sit in front of your house and take pictures and camp out all day," marvels Taylor of Hanson's mostly young, female audience. "Four or five cars will just sit there." But he's quick to add, "Having fans like that is what keeps you able to do it, having fans that will stay up all night to get tickets for a concert."

Facing the roar of thousands of screaming teenage fans is still a bit unreal to the Hansons. Their disciples pack their every concert appearance and write tearstained letters. During a recent trip to Indonesia, a crush of overzealous fans tore at the Hansons' clothes and hair. Their 9-year-old sister, Jessica, has since told her brothers,

"Girls are weird."

"It's very cool to experience that," says Isaac, his smile showing more braces than teeth. "It's a humbling experience, because you don't witness that often. So it's like, 'Whoa! Why is this happening? I don't deserve this.' People are just so ecstatic about meeting you or being at the show."

The trend is unlikely to end soon, with Hanson's first national concert tour set to begin in the spring. Today's photo shoot is designed to produce enough posters and T-shirts to keep the bands rabid fans satisfied until then. Off to the sides stands the boys' father, Walker Hanson, forever brandishing a video camera and a bag of his own photography equipment.

The Hansons enjoy the relatively restful day of posing. Soon enough they will begin preparing for the Grammys, where they're nominated for Record of the Year ("MMMBop"), Best New Artist and Best Pop Performance by a Duo or Group. Their biggest dilemma is whether to perform the ubiquitous "MMMBop" or their new single, "Weird."

"It's going to be awesome," Taylor says. "People say, 'Do you think you're going to win?' You can't know. We're just going to go there and enjoy the experience."

Now the Hansons are back in their Los Angeles hotel suite, drinking Diet Cokes and turning another interview into another chance for goofing off. Slouching in his chair Zac holds an empty glass to his eyes. In this company it's hard to get lonely, even when far from home. "We're buds, we're friends, so we get along very well," says Isaac. "That makes it easier."

Lately, these brothers have been spending more time in places like Los Angeles and New York City then they have in Tulsa. It wasn't so long ago that Hanson was singing a cappella for fun in pizza parlors and then at county fairs, inspired by classic pop and R&B from the '50s and '60s, from Otis Redding to the Beatles. Hanson learned to appreciate the roots of pop when their father, then an oil-industry consultant, took the family to live in Venezuela and Ecuador for a year, and all they had to listen to was a cassette of 1958 rock & roll. "When everybody else was listening to MC Hammer and Vanilla Ice, we were into Bill Haley and Carl Perkins," says Taylor.

On their return to Tulsa, they soon discovered the contemporary rock of Counting Crows and Spin Doctors but never lost their taste for pluperfect pop. Both parents had studied music and passed on those musical tendencies to their kids as part of their homeschooling. After signing a contract with Mercury Records, Hanson arrived in Los Angeles to work with a variety of accomplished producers, including the Dust Brothers (who worked with Beck, the Rolling Stones and many others).

The massive popularity that followed came as a complete shock, the boys say now. "How could you possibly expect that to happen?" says Isaac. "It really hit us," says Taylor, "when we turned on the radio and heard Casey Kasem saying, 'Here's Hanson!' And the fans! We'd go somewhere, and thousands of people would show up to see us play three songs." New fame does have its perks. For Hanson, that includes the chance to meet people like Jewel, Neve Campbell and No Doubt's Gwen Stefani. They've also been offered a variety of TV and film projects-everything from a Barney special to a splatter horror film-all of which they've wisely turned down.

Instead, the band prefers to plan the recording of their next album later this year, a project they hope will establish them as serious musicians, and not one-hit wonders. "We've been writing all through the year, thinking about the next album," says Taylor. "We're not buying expensive cars. We're investing our money in continuing, maybe having a studio, things that are very essential and not extravagant at all. We just hope we can keep doing it."

Pretty mature for a 14-year-old.