Over half of the persons infected with the lymphadenopathy-associated virus/human T-lymphotropic virus type III (LAV/HTLV-III), the retrovirus that causes the acquired immunodeficiency syndrome (AIDS), become persistently infected with the virus. These "carriers" serve as the major reservoir of infection for others. Virus from their vascular and lymphatic spaces infects others through direct blood or mucous membrane exposure. After months to years, a high proportion of those infected will develop clinical manifestations of infection. For infected homosexual men, approximately 25% have developed AIDS-related conditions, mainly lymphadenopathy, and approximately 10% have developed AIDS. Because of the large number of infected persons in the United States, increasing rates of disease can be expected.