Serious fungal infections are significant complicating and life-threatening occurrences in patients with advanced HIV infection. Oropharyngeal candidiasis is found in almost all such patients, and causes pain, difficulty in swallowing, and loss of appetite. Similarly, esophageal candidiasis causes illness in the population. Cryptococcosis, endemic mycoses, and coccidioidomycosis also cause significant illness and death in AIDS patients. Once established, fungal infections in AIDS patients generally require continuous suppressive therapy because attempts at curing these infections are usually unsuccessful. Fluconazole has a number of characteristics that would make it a logical candidate to examine as a prophylactic agent in patients with advanced HIV infection. Animal studies have shown it to be prophylactic in models of candidiasis, cryptococcosis, histoplasmosis, and coccidioidomycosis. Initial experience in patients with active cryptococcal meningitis appears favorable, and studies of oropharyngeal candidiasis show it to be effective.