The acquired immunodeficiency syndrome (AIDS), as defined according to the criteria from the Centers of Disease Control, is a state characterized by one or more opportunistic diseases indicative of underlying cellular immunodeficiency in absence of other underlying causes of cellular immunodeficiency than HIV infection and in absence of all other causes of reduced resistance reported to be associated with opportunistic diseases. The opportunistic diseases in AIDS include opportunistic infections and neoplasms that can result from immunodeficiency. AIDS is caused by a retrovirus which has recently been renamed human immunodeficiency virus (HIV). This virus had previously been designated human T cell lymphotropic virus type III (HTLV-III), lymphadenopathy-associated virus (LAV), and AIDS-related virus (ARV). High-risk groups in non-Third World countries have been defined as homosexual or bisexual males, intravenous drug abusers, immigrants from Haiti and Central Africa, blood transfusion recipients, heterosexual partners of AIDS patients, children of mothers with AIDS, and hemophiliacs who have received factor VIII concentrate. About 72% of the AIDS patients originate from the first mentioned risk group, 17% from the second risk group. The other risk groups constitute only minor percentages of the total AIDS patient population. The incidence of AIDS appears to be increasing rapidly. The 3-year mortality rate is 90%.