A proportion of the plasma for the triply inactivated, plasma-derived hepatitis B vaccine produced in the United States is obtained from homosexual men. Because homosexual men are a high-risk group for the acquired immunodeficiency syndrome (AIDS), concern has emerged that the vaccine could harbor the AIDS agent. To evaluate this risk, we tested 15-month postvaccination serum samples for antibodies to human T-cell lymphotropic virus type III in 100 health care workers who had received inactivated hepatitis B vaccine lots made from plasma collected between 1977 and 1979 and 100 who had received placebo injections. None of the 200 health workers had serological evidence of human T-cell lymphotropic virus type III infection. These serological findings lend additional support to earlier epidemiologic and immunologic observations suggesting that hepatitis B vaccine does not transmit infection with an AIDS virus.