In the summer of 1981, the Centers for Disease Control (CDC) alerted the medical community to an unexpected outbreak of Pneumocystis carinii pneumonia and Kaposi's sarcoma in young homosexual men, individuals not known to be at risk for these uncommon diseases. Studies of immunologic functions in these patients demonstrated lymphopenia, cutaneous anergy, reduced helper T-lymphocyte (T4) subpopulations, depressed ratios of helper T-lymphocytes to suppressor T-lymphocytes (T4:T8), abnormal lymphocyte responses to mitogen stimulation, decreased natural killer-cell activity, and often hypergammaglobulinemia. The name of acquired immunodeficiency syndrome (AIDS) was given to this disorder of immunologic regulation with opportunistic infections or Kaposi's sarcoma or both.