Secondary infections remain the leading cause of death in patients with the acquired immunodeficiency syndrome (AIDS). Dealing with the rapidly evolving spectrum of infectious problems seen in patients with AIDS requires knowledge of current therapeutic and prophylactic strategies. Through an extensive preclinical trials network supported by both industry and government, an increasing number of new agents are being identified and rapidly moved into clinical trials. Several agents are now available to treat diseases caused by Pneumocystis carinii, and corticosteroids have become a useful adjunct to antimicrobial agents in the treatment of P. carinii pneumonia. Although the treatment of toxoplasmosis remains a challenge, alternatives to sulfadiazine and pyrimethamine are now available. Mycobacterial infections, particularly with Mycobacterium tuberculosis, have become an increasing problem for patients with AIDS, and both old and new combination drug regimens are being used. Cytomegalovirus disease, until recently an untreatable problem, can now at least be partially managed with antiviral agents. The use of more complete prophylactic regimens may decrease the morbidity and mortality from opportunistic infections.