Because of past multiple exposures to contaminated coagulation factor concentrates, the prevalence of human immunodeficiency virus (HIV) infection among adult hemophilic men in the United States is reported to range from 75 to 90 percent. The risk of HIV transmission through a long-term monogamous heterosexual contact can be estimated by studying the spouses of hemophilic subjects since these couples generally do not abuse intravenous drugs, usually maintain stable monogamous relationships, and are usually free of other risk factors. Our purpose was to gather data on the risk of heterosexual transmission of HIV infection in the context of long-term monogamous relations according to the duration of HIV antibody seropositivity and of HIV antigenemia in HIV-infected hemophilic men, and their sexual habits. Infection with HIV was studied in 14 sexually active spouses of infected hemophilic men who had been HIV antibody reactive for a mean of 46 +/- 23 (SD) months. One half of the hemophilic men studied had overt HIV antigenemia for a mean duration of 27 +/- 23 (SD) months; six of the men studied fulfilled clinical criteria for the diagnosis of acquired immunodeficiency syndrome (AIDS). All 14 couples were sexually active in a strictly monogamous fashion, in marriages of 13.5 +/- 10.5 (SD) years with an average reported frequency of four sexual encounters per month (range: one to 12). Plasma samples of the hemophilic husbands were retrospectively analyzed for HIV and hepatitis B virus markers. Blood samples were obtained from female spouses on at least two occasions, six months apart. Comprehensive questionnaires regarding sexual habits and other risk factors were filled out by each couple; during this interview, the couple was counseled about safe sexual practices. None of the couples studied used condoms prior to January 1986. Antibodies to HIV developed in only one of the 14 wives. At the time when this seroconversion was detected, her husband, in whom AIDS developed, had been reactive for HIV antibody for 49 months, and showed positive findings for HIV antigen for 26 months. No additional risk factors were identified for this couple. The infected female spouse, however, has a 14-year history of multiple sclerosis, and had been treated with immunosuppressant intermittently. Despite a significantly reduced number of CD4 lymphocytes, she has remained clinically asymptomatic for 17 months since seroconversion. HIV antibodies did not develop in any of the 13 remaining wives, despite the frequent practice of oral sex by six couples and reports of occasional anal intercourse by another couple.(ABSTRACT TRUNCATED AT 400 WORDS)