Chris Kelly, 34, half of the 1990s kid rap duo behind one of the decade's most memorable songs, "Jump," died Wednesday at an Atlanta hospital of an apparent drug overdose, authorities said.

Mr. Kelly, known as "Mac Daddy," and Chris Smith, known as "Daddy Mac," made up the rap group Kris Kross and were known for wearing their pants backwards as they rhymed.

No official cause of death had been determined, pending a toxicology screening. However, "it appears it may have been a possible drug overdose," said Cpl. Kay Lester, a spokeswoman for the Fulton County police.

Kris Kross was introduced to the music world in 1992 by music producer and rapper Jermaine Dupri after he discovered the pair at Greenbriar Mall in southwest Atlanta.

"To the world Chris was Mac Daddy but to me, he was a son I never had . . . ," Dupri said in a statement Thursday. "When I think about it, I spent more time with Chris and Chris than damn near anybody in my whole life, so you can imagine how bad this hurts."

Dupri added, "I will always love you Chris, and I will never let the world forget you, may God bless your soul."

Their first, and by far most successful, song was "Jump." It was one of four hit singles on their 1992 debut album, Totally Krossed Out, which sold four million copies; like all three of their studio albums, it was released on Conshohocken's Ruffhouse Records.

"Jump" featured the two trading verses and rapping the refrain, the song's title. The duo had surprising maturity in their rap delivery, though the song was written by Dupri. It would become a No. 1 smash in the United States and globally, and one of the most popular of that year.

Their success led to instant fame: They toured with Michael Jackson, appeared on TV shows, and even had their own video game.

The group was never able to match the tremendous success of their first song, though they had such other hits as "Warm It Up" and "Tonite's tha Night."

In 2009, after photos surfaced that showed Mr. Kelly with bald spots on his head, there were rumors that he had cancer. But in an interview posted on YouTube by Straight from the A TV, he said he suffered from alopecia, a condition marked by hair loss.

"My health is good, I just got alopecia. I don't have cancer, no other sort of diseases," he said.

According to a Fulton County police report, Mr. Kelly's mother, Donna Kelly Pratte, and an uncle told authorities that Mr. Kelly had a history of drug abuse and experienced overdoses in the past.

Earlier this year, Mr. Kelly and Smith performed together to celebrate the anniversary of Dupri's label, So So Def.