To evaluate the risk of heterosexual transmission of the acquired immunodeficiency syndrome, lymphadenopathy, and infection with human T-lymphotropic virus type III (HTLV-III), we studied 42 hemophiliacs and their wives. By early 1984, 9 of the hemophiliacs had asymptomatic lymphadenopathy and 1 had the acquired immunodeficiency syndrome. Twenty-one hemophiliacs, including all 10 with clinically overt disease, had antibody to HTLV-III. None of the 42 wives had lymphadenopathy or the acquired immunodeficiency syndrome but 2 had HTLV-III antibody. One of these women had evidence of immunologic dysfunction with a markedly reduced T-helper/suppressor cell ratio. The husbands of these 2 women both had HTLV-III antibody, but neither had overt acquired immunodeficiency syndrome-related disease. Thus, as of early 1984, the prevalence of HTLV-III antibody in wives of hemophiliacs seropositive for HTLV-III was 9.5% (2 of 21). We conclude that transmission of HTLV-III occurs between hemophiliacs and their heterosexual partners.