We report four cases of immunologic thrombocytopenic purpura related to human immunodeficiency virus (HIV) transmitted through heterosexual contact in persons who were not homosexual, addicted to intravenous narcotic drugs, or hemophilic. Each transmission occurred in a different setting. A 23-year-old white woman had immunologic thrombocytopenic purpura in July 1985, with a platelet count of 11 X 109/L. In January 1987, she had prominent submandibular and posterior cervical adenopathy. A careful social-sexual history revealed several sexual contacts with a male narcotic addict before July 1985. A 27-year-old heterosexual white man had a platelet count of 8 X 1099/L in December 1986. A social-sexual history revealed that his fiancée had been an intravenous narcotic addict 6 years ago. A 64-year-old white woman had a platelet count of 75 X 109/L in May 1986, approximately 2 years after she had resumed having sexual intercourse with her husband who had had a triple coronary bypass in October 1983. The husband had received HIV-seropositive blood. A 42-year-old white man had a platelet count of 45 X 109/L, which was associated with a cutaneous eruption refractory to antibiotics and antifungal agents. He had had sexual contacts with several women, who, to the best of his knowledge, were neither prostitutes nor intravenous narcotic addicts. He denied homosexuality or drug abuse. All four patients were HIV-seropositive and had circulating immune complexes and platelet-associated IgG, C3C4, and IgM values that were considerably higher than those usually measured in patients with classic autoimmune thrombocytopenia, averaging 2.4-, 2.2-, 6.5- and 5.2-fold higher, respectively. Thus, HIV-related immunologic thrombocytopenic purpura can be heterosexually spread and should become part of the differential diagnosis of unexplained thrombocytopenia. Obtaining a careful social-sexual history is mandatory in such patients.