Last week, Caplan, 50, earned the dubious distinction of being the first prominent bioethicist to get sued for his advice. The father of Jesse Gelsinger, an 18-year-old from Arizona who died a year ago during experimental therapy for his inborn metabolic disorder, named Caplan in a lawsuit against several Penn doctors and two hospitals.

Some bioethicists worry that the lawsuit could stifle ethical debate. Many feel that it represents a coming of age of sorts for bioethics, an academic field that began in the 1960s and whose influence has exploded along with changes in medical technology.

"Over the past five to 10 years, people have begun to realize that bioethics is developing into a discipline. Maybe one of the signs of reaching that status is getting sued," says Gilbert Mailaender, a bioethics professor at Valparaiso University in Indiana.

In the past 30 years, bioethics has become a new priesthood, replacing the clergy in the provision of advice about life-and-death issues. Working out of more than 150 U.S. academic centers, bioethicists help doctors and researchers make difficult decisions such as whether to resuscitate brain-damaged preemies or how to keep patient records private while examining DNA. Bioethicists' wisdom is sought by Congress on cutting-edge issues like human cloning, embryo research and artificial intelligence. In 1995, President Clinton created the National Bioethics Advisory Committee as a standing debate club for biomedical questions.

Most recently, bioethicists have played a crucial role in efforts to reform institutional review boards or IRBs, the overworked university panels that are sometimes criticized for their lack of independence from the researchers they oversee. IRBs are required to examine all federally funded research designs for safety and worthiness.

It was the Gelsinger case that propelled IRB reform. And ironically, Caplan has done as much as any bioethicist to push the IRB reform agenda, especially in assuring informed consent -- the requirement that researchers fully explain the possible risks and benefits of an experimental therapy to their subjects.

While Gelsinger gave informed consent, the complaint charges that researchers left out a few crucial details on the possible risks involved in the study. These risks, the family claims, might have swayed Gelsinger from participating. Making sure patients are capable of understanding the risks is why Caplan gave the advice he did: Enroll only consenting adults.

Initially, gene therapy researchers at Penn planned to carry out their experiments on fatally ill babies suffering from the rare metabolic disease ornithine transcarbamyulase deficiency. Caplan advised against it. Older, healthier children or adults were more appropriate research subjects, he argued -- babies can't give informed consent, and their parents are too grief-stricken to give fully reasoned informed consent.

Paul Gelsinger charges in his complaint that Caplan's advice led to the recruitment of his son for the gene therapy trial -- and thus indirectly killed him.