A role for the biological effects of alcohol is postulated in the increased risk of AIDS known to be associated with chronic alcohol abuse and alcohol consumption during sexual activity. In pilot experiments peripheral blood mononuclear cells from healthy volunteers were studied before and after a single ingestion of 0.7 to 3.1 liters of beer or an equivalent dose of ethanol in other beverages. After moderate alcohol consumption there was increased human immunodeficiency virus (HIV) replication in peripheral blood mononuclear cells during 28 days of culture without mitogen stimulation as indicated by overnight syncytium formation with SUP-T1 indicator cells and by increased levels of HIV p24 antigen in the culture supernates. There was also decreased ability of lymphocytes to produce interleukin 2 and soluble immune response suppressor activity after stimulation with concanavalin A, the former, possibly both, for over 4 days after alcohol ingestion. These preliminary data extend well-known immunosuppressive effects of chronic alcohol ingestion to acute ingestion and raise the question: Could even casual alcohol consumption enhance HIV infectivity and/or enhance the progression of latent HIV infection?