BOSTON (ITN) * Harvard Medical School has decided not to censure a Pulitzer Prize-winning professor who studies people who say space aliens abducted them for sexual experiments.

However, psychiatrist Dr. John Mack received an unusual public warning from the dean not to let his enthusiasm for UFO research steer him from the path of professionalism.

The decision disclosed Thursday followed a one-year investigation that Mack's lawyer called a challenge to academic freedom.

"This is the type of thing that almost by its existence can be intimidating," Roderick MacLeish said.

Mack's fellow professors supported him for fear that they might be next in line for scrutiny, MacLeish said. All members of the faculty contacted by The

Associated Press during the investigation refused to speak for the record. The review began after Mack appeared on "Unsolved Mysteries" and other TV programs to promote his 1994 book "Abduction: Human Encounters With Aliens," about his patients, including a man who remembers an alien female extracting a sperm sample from him, a woman who says she gave birth to a human-alien hybrid and a man who says he had an alien wife in a parallel universe.

The faculty committee investigated whether Mack's work met professional standards and whether it could be considered research on human subjects, which requires special permission.

"It was not our function to describe whether John Mack's astonishing claims are true," said the chairman, Dr. Arnold Relman, a former editor of The New England Journal of Medicine.

"All we were asked to do was to determine whether he was using the kind of scholarship and rigor and commitment to the evidence that one would expect of a member of the Harvard faculty," he said.

Medical school spokeswoman Keren McGinity declined to say how often such investigations are conducted. The school would not release the findings and McGinity refused to answer questions.

Mack, 65, was traveling Thursday and could not be contacted, an assistant said. In an interview last year, he said that he does not necessarily believe in space aliens but thinks that some unknown traumatic experience explains his patients' memories.

"All that he was basically saying was that there were some mysteries in life," MacLeish said. "He was not vouching for the kind of testimony these people have been making, just that they did not appear to be mentally ill."

Mack founded the psychiatry department at Cambridge Hospital, one of Harvard's teaching hospitals, and is director of the Program for Extraordinary Experience Research at the Harvard-affiliated Center for Psychology and Social Research. He won a Pulitzer Prize in 1977 for his biography of Lawrence of Arabia.

Some colleagues were reportedly unhappy that Harvard's name became associated with Mack's study of 120 patients who say aliens took them away in flying saucers for sexual experiments.

Mack said last year that his colleagues were too quick to dismiss his work. "We don't have room in our culture for this," Mack said. "It's the elite people, my colleagues, who decide what we're supposed to believe, and to them this isn't supposed to be."