Baby Fae, the world's longest surviving human recipient of an animal heart, has shown the first signs of rejecting the baboon heart implanted in her chest 17 days ago, one of her doctors said yesterday, adding that a new transplant is possible.

Dr. Robin Doroshow, a pediatrician at Loma Linda University Medical Center in California, said the baby is receiving increased doses of a drug that suppresses her still underdeveloped immune system, as the first step to fight the rejection.

"We have diagnosed an episode of rejection and have already started treating her," Doroshow said from Los Angeles on "Face the Nation" (CBS, WDVM). "She is showing a good response to treatment."

If the infant's rejection of the heart cannot be controlled with drugs, another transplant is possible, Doroshow said. Her name has been entered in the national registry as a candidate for a human heart transplant, but Doroshow added that "baboon hearts will be available if the appropriate human heart cannot be located."

A second baboon heart would come from the colony of baboons at the Loma Linda laboratory east of Los Angeles. Baby Fae's operation was the first of what were to be six such transplants.

The experimental transplant -- the first involving an animal's organ and a human infant -- has drawn criticism from medical-ethics and animal-rights advocates. The experiment also has raised questions about whether a human heart was available, whether alternative procedures were possible and what Baby Fae's parents were told beforehand.

The human body's natural defense mechanisms normally would reject a transplanted organ, but Baby Fae has been receiving a drug, cyclosporin-A, that essentially suppresses her immune system while not leaving her susceptible to major diseases. Doroshow said "we're certainly being very vigilant for evidence of infection" as the drug dosage is increased to ward off rejection.

Doroshow said doctors "a couple of days ago" noticed the first signs that the baby's body was rejecting the baboon heart. The rejection process was confirmed within the last 48 hours, the doctor said.

The infant, whose identity has been kept private, is no longer receiving extra oxygen from a ventilator. "To look at her she appears normal," Doroshow said. "She continues to do very well physically."