Prevention of the transmission of the acquired immunodeficiency syndrome (AIDS) by transfusion has been the most successful area of epidemiologic control of the disease. Only 2% of the more than 50,000 cases reported to the Centers for Disease Control (CDC) have been attributed to transfusion, and the vast majority of these patients were infected before the introduction of screening tests in April 1985. The overall prevention program involves donor education, adequate medical history, physical examination, and mechanisms that allow exclusion of individuals at risk in a confidential manner. The current screening tests for human immunodeficiency virus (HIV) antibodies are highly sensitive, and the Western blot confirmatory test is highly specific. The present program can be used as a model in screening for other viruses and diseases, and its success has stimulated current work in developing multiple-retrovirus screening tests to detect either several retroviruses simultaneously or elements that are common to all retroviruses.