Along with homosexual men, Haitians, and intravenous drug abusers, hemophiliacs are at high risk of contracting acquired immunodeficiency syndrome (AIDS). An earlier study revealed that 36 percent of a group of the AIDS patients had antibodies to cell membrane antigens associated with the human T-cell leukemia virus (HTLV-MA), whereas only 1.2 percent of matched asymptomatic homosexual controls had these antibodies. In the present experiments, serum samples from 172 asymptomatic hemophiliacs were examined for the presence of antibodies to HTLV-MA. Such antibodies were detected in 5 to 19 percent of the hemophiliacs examined from four geographical locations, but in only 1 percent or less of laboratory workers, normal blood donors, donors on hemodialysis, or donors with chronic active hepatitis.