The problem of human immunodeficiency virus (HIV) infection and that of the acquired immunodeficiency syndrome (AIDS) are becoming increasingly important in clinical transplantation. The epidemiologic characteristics of this infection are important factors in determining the impact of this infection on transplant patients: in particular, the presence of a transmissible virus in the blood, tissues, and body fluids of even asymptomatic individuals for prolonged periods; the role of lymphocyte activation in accelerating the pace and effects of HIV infection, with the transplant patient having more reasons for lymphocyte activation than other patient categories; and the possible contributions of immunosuppressive therapy to the course of HIV infection. Already, at least 20 cases of primary HIV infection conveyed by infected blood or allografts at the time of transplant have been noted; a similar number of transplants have been carried out in asymptomatic carriers of the virus. The initial impression is that the course of HIV infection in these patients is accelerated, but information is incomplete and an international registry for the study of this problem has been established.