More than a million Americans are infected with the human immunodeficiency virus (HIV, formerly HTLV-III/LAV), and their risk for the acquired immunodeficiency syndrome (AIDS) may exceed 30% (1, 2). Physicians in clinical practice must be prepared soon to counsel and care for persons identified as infected through the large HIV screening programs of the American blood and plasma collection agencies and armed forces (3, 4). Physicians also will need to use and interpret HIV assays as these tests become part of standard medical practice in the care of drug users, hemophiliacs, and homosexually or heterosexually active adults, as well as