Candida lusitaniae associated with infection in a patient with acute myelogenous leukemia developed resistance to amphotericin B during systemic treatment of the patient. The organism, when isolated initially, was inhibited by 0.31 mug of amphotericin B per ml in yeast nitrogen base agar, but when isolated (20 days later) just antemortem and postmortem, required 100 and 50 mug/ml, respectively, for complete inhibition at 48 h.