Treatment of 39 patients indicates that intravenous amphotericin B is effective for the therapy of blastomycosis, cryptococcosis, histoplasmosis, and sporotrichosis. Its ultimate place in the treatment of systemic coccidioidomycosis and candidiasis remains to be determined. Amphotericin B in its present form is suitable for intravenous, intrathecal, and local instillation. The side effects of intravenous amphotericin B are many and sometimes serious. Severe side effects are usually ameliorated by hydrocortisone or prednisolone. The toxicity of intravenous amphotericin B is greatest for the kidney. Increased excretion of potassium and reduced urea clearance are the most obvious manifestations of renal toxicity.