Pneumocystis carinii pneumonia (PCP) is the most common opportunistic infection in patients with AIDS, accounting for significant morbidity and mortality. Clinical data indicate that staining induced sputum provides a sensitive, noninvasive technique for the rapid detection of PCP. AIDS patients with PCP and worsening respiratory distress, increasing pulmonary infiltrates and respiratory rate, and worsening arterial oxygenation may gain significant benefit from the addition of corticosteroids to their therapy. Serious life- or sight-threatening cytomegalovirus disease is an often recognized, but difficult to manage infectious complication of AIDS. The only effective therapy involves ganciclovir, and possibly foscarnet, although both antiviral agents are limited by toxicities and the necessity for intravenous infusion. Antiviral therapy generally offers hope for inhibiting virus-induced immunosuppression. Since the beginning of the AIDS epidemic, mycobacterium avium intracellulare (MAI) complex has been frequently identified in patients with AIDS. Interaction between the HIV virus and syphilis represents an additional treatment challenge. Cryptococcosis is also a life-threatening infection among AIDS patients that is difficult to treat. Oral lesions are common in patients with combined immunodeficiency syndromes, specific T-cell deficiencies, and diseases associated with defects in phagocytic cell mechanisms. Early diagnosis of AIDS can be made by recognizing the salient features of intraoral neoplasms. References, tables.