Developing shingles between the ages of 20 and 50 may herald the beginning of acquired immune deficiency syndrome among people at high risk for the deadly disease, a new study reports.

At New York University Medical Center, researchers studied 48 patients with shingles -- 41 of whom were in a high-risk group for AIDS, which includes homosexual and bisexual men and intravenous drug users.

Blood tests on all but one of the people in the high risk group revealed the presence of antibodies to HTLV-3, the virus that causes AIDS. But none of the seven shingles patients who were not in the high-risk group had the antibodies.

"If these people had not developed herpes zoster shingles they would not have known" that they had been exposed to the AIDS virus, said Dr. Alvin Friedman-Kien, a coauthor of the study, which is scheduled to be presented Friday at the Society for Investigative Dermatology's annual meeting in Washington. "They had no underlying evidence of AIDS. They were healthy people." Getting shingles, Friedman-Kien said, was otherwise "unexplained."

Two of the 41 people in the high-risk group were intravenous drug users and 39 were either gay or bisexual men. The remaining seven participants in the study were heterosexuals and had no history of drug use. All participants were between the ages of 20 and 50 -- an early time for shingles to strike.

Of the 40 people who had antibodies in the blood for HTLV-3, seven developed full-blown AIDS during the next two years. About a year and a half into the study, the remaining patient in the high-risk group had a positive test for the HTLV-3 virus, and then one month later developed Kaposi's sarcoma and full-blown AIDS.

"In patients at risk for AIDS," Friedman-Kien said in an interview, "the occurrence of shingles may be one sign that heralds the marked depression of the immune system associated with AIDS. Doctors should be alerted to the fact that shingles in high-risk groups may be a sign of impending AIDS."

Shingles is caused by the same virus that produces chicken pox. Known as herpes zoster, the illness generally occurs decades after a person has had chicken pox.

Shingles "is uncommon" among people with well-functioning immune systems, Friedman-Kien reports in an upcoming article on the study set for publication in the May issue of the American Journal of Dermatology. Studies in England and in Minnesota suggest that among younger adults, those 20 to 50 years of age, the annual incidence of shingles is only one to three cases per 1,000 people.

In between the childhood onset of chicken pox and the development of shingles, the virus is thought to lie dormant in nerve cells throughout the body. Once reactivated, it produces crops of painful skin lesions, resembling small blisters. At the same time, nerve cells become inflamed and often die.

Friedman-Kien began the study of shingles patients after noticing the high incidence of shingles among AIDS patients. In a previous study of 300 AIDS patients, Friedman-Kien and his colleagues found that patients with Kaposi's sarcoma -- a deadly form of cancer that afflicts AIDS patients -- were seven times more likely to have had shingles in the past three years than other people.