NEW YORK - The Black Eyed Peas spent years languishing in hip-hop's underground before they found the formula to vault them into the mainstream - accessible pop melodies, star collaborations, marketing tie-ins and a sexy young thing to belt out catchy choruses.

That mix made their 2003 album Elephunk their big breakthrough. Their first two albums failed to sell 500,000 copies combined. Elephunk, however - which featured the Grammy-nominated anthems Where Is the Love with Justin Timberlake and Let's Get It Started, which became the National Basketball Association's playoff anthem - went multiplatinum and made them and their music ubiquitous.

Still, there are plenty of early Peas-heads who remain disgruntled about the group's leap to the pop world.

Go ahead and call them sellouts, though. Lead lyricist will.i.am (Will Adams) doesn't mind.

"It's cool. It makes me feel good because that means they really liked our first record," he said.

And then the group breaks out into uproarious laughter.

The Black Eyed Peas have plenty to be merry about these days. Coming off a Grammy this year and the success of Elephunk (2.7 million copies sold) the foursome should prove that they aren't a flash in the pan with their latest album, Monkey Business. The disc, which again features Mr. Timberlake, along with the Godfather of Soul, James Brown, sold 291,000 copies in its first week of release, according to figures released Wednesday. The funky first single from the album, Don't Phunk With My Heart, already is a Billboard top 10 hit.

Amy Doyle, MTV's vice president of music and talent programming, says the key to the Black Eyed Peas' success is their ability to "straddle a wide audience ... their music is not polarizing."

"It's really all about the catchy songs that they write that get stuck inside everybody's head as well as a real vibrant live performance," she said. "And they always deliver really good videos, too."

The Los Angles-based group, which started out years ago as the trio of will.i.am, apl.de.ap (Allan Pineda) and Taboo (Jaime Gomez), first came onto the scene as an effervescent band that melded eclectic hip-hop beats with lyrics that sometimes were socially relevant, sometimes irreverent, but definitely apart from the sex and violence that permeates much of rap and hip-hop.

Critics loved it, and they had a strong following.

"When I go back then, and I think about our careers, I think we were pretty successful," says will.i.am, the most talkative member of the group, as they sit backstage waiting to perform at an MTV event.

Their debut CD, 1998's Back to Front, had modest success, but the weak response to the follow-up, Bridging the Gap, left them feeling particularly defeated, and they fell into destructive habits.

"Me and Tab were going out drinking every night," will.i.am says.

Eventually, the band decided to put all their focus into Elephunk, which they saw as potentially their last album. Not everyone was quite as willing to straighten up, though.

"He got mad at us because we took him to rehab," will.i.am says of Taboo, as they all start to laugh.

"Because they told me they would take me shopping!" Taboo cries out - to the laughter of the group again.

Besides getting themselves together, they also decided to tinker with their sound.

A female vocalist they used on tracks had left, so they found Fergie (Stacey Ferguson) - a former member of Wild Orchid, which had modest success in the 1990s.

Joining three guys who had been together for years wasn't easy for Fergie.

"It was like a gradual progression for me on stage, because they had been together for years. I'm coming onto the stage, not really knowing where I fit in. So I kind of had to sit back and watch and find my niche in the band," she says.

"I think Fergie rounded out the package," Ms. Doyle says.

"They were always a very talented group but when they added Fergie they added another dimension. And then their songwriting definitely got better over time. They were able to capture the lighter side of a hip-hop audience as well as bridge the gap between hip-hop and pop with a very unique sound."

Some critics, however, saw it as a blatant attempt to cross over. Given that their music has always been more palatable to club lounges than the gritty streets, it added even more fodder to those who considered the group watered-down hip-hop.

Those criticisms irritate will.i.am a little - but just a little.

"What's hip-hop?" he asks.

Jim Cooper/associated pressThe Black Eyed Peas are Fergie (Stacey Ferguson, from left), Taboo (Jaime Gomez), apl.de.ap (Allan Pineda) and will.i.am (Will Adams).