The treatment of most fungal infections is difficult, at best. Antifungal therapy is complicated by the development of resistant organisms and by the toxicity of many agents. Ketoconazole, an orally active imidazole derivative, has been approved by the Food and Drug Administration for the treatment of candidiasis, chronic mucocutaneous candidiasis, oral thrush, candiduria, coccidioidomycosis, histoplasmosis, chromomycosis, and paracoccidioidomycosis. At present, there is very little peer review literature on ketoconazole's effectiveness for several of its approved indications. Gastrointestinal side effects account for the majority of reported adverse reactions; however, preliminary evidence suggests that higher dosages of ketoconazole may decrease adrenal steroidogenesis. Currently, ketoconazole 200-400 mg/d is recommended; the duration of therapy remains to be firmly established. Until well-designed clinical trials are completed and ketoconazole's effectiveness is compared to that of established antifungal agents, its use should be limited.