HIV infection is diagnosed by demonstration of specific antibodies. During the acute HIV disease such antibodies are not yet detectable. So-called early manifestations are confined to skin and mucous membranes, in fact appearing several years after virus inoculation. Antiviral therapy with early intervention aims at the prevention of immunodeficiency. The achievement of prolongation of survival has been proven in controlled studies with azidothymidine (AZT). Several studies with low dose and early intervention have shown 500 mg/day to be the standard dose and to be efficacious in asymptomatic patients with CD4 cell count below 500/microliters. New studies have shown that combination therapy with different drugs might be superior to monotherapy with AZT.