CHICAGO (AP) _ The 3-year-old boy who received part of an adult liver to replace his diseased organ went home from the hospital Saturday, and doctors say his case is a good sign for other children awaiting liver transplants.

The operation Jan. 19 at the University of Chicago Medical Center was the first time doctors in the United States successfully transplanted a portion of an adult liver into a child, hospital spokeswoman Gretchen Flock said Saturday.

Similar transplants had been successfully performed in Europe, but the few previous attempts by American doctors had failed, she said.

Doctors are optimistic that John Genna will lead a normal life and, because the liver easily regenerates itself, the doctors hope the transplant will function as a permanent organ, Ms. Flock said.

Linda Genna said she and her husband, Joseph, were ''ecstatic'' over their son's improvement. The boy was admitted to the hospital Jan. 17 in a deep coma, suffering from acute hepatitis, said Ms. Flock.

The liver of a 24-year-old man who died in Las Vegas, Nev., became available and was flown to Chicago.

''To see him the way he is now, it's like one extreme to another,'' Mrs. Genna said. ''He's just really doing great. It's just unbelievable.''

The Gennas decorated their house in suburban Cicero with balloons and ''Welcome Home'' signs.

''He just really happy to be home,'' Mrs. Genna said.

The success of the boy's operation ''could open up a whole pool of available livers for children,'' Ms. Flock said. ''At this point, about 50 percent of children waiting for livers die'' because of a shortage of child donors, she said.

Doctors originally had anticipated using the adult segment as a ''bridge'' until a child-size liver became available and a second transplant could be performed, said Dr. Christoph Broelsch, who headed the team that operated on the boy.

But doctors now believe a second transplant won't be necessary, Ms. Flock said.