Because the current outbreak of acquired immunodeficiency syndrome (AIDS) among previously healthy adults may be caused by a transmissible biologic agent, and because it may be preceded by immunologic abnormalities with or without a prodromal illness, we studied seven female sexual partners of male patients with the syndrome. The male patients were all drug abusers. One of the seven women was found to have the full-blown syndrome, a second had an illness consistent with the prodrome of AIDS (generalized lymphadenopathy, lymphopenia, and a decreased ratio of helper to suppressor T cells), and four others had generalized lymphadenopathy or lymphopenia, with or without a decreased ratio of helper to suppressor T cells. Only one woman had no abnormalities. These findings suggest that AIDS may be transmitted between heterosexual men and women.