To study the effectiveness, safety, and tolerance of fluconazole versus clotrimazole troches (lozenges) as prophylaxis (preventive treatment) against fungal infections in patients enrolled in ACTG 081 (a study of prophylaxis against pneumocystosis, toxoplasmosis, and serious bacterial infection). Primarily, to compare the rates of invasive infections by C. neoformans, endemic mycoses, and Candida. To compare the mortality rates due to fungal infections between two antifungal prophylactic treatments. Secondarily, to assess the effect of prophylaxis on the incidence of severe fungal infections, defined as invasive infections and esophageal candidiasis and less severe mucocutaneous infection.