Serum levels of amphotericin B were serially determined during and after a course of therapy in an anephric patient who developed systemic candidiasis after an unsuccessful renal transplantation. There was no progressive accumulation of drug in serum, and the pattern of disappearance of drug from serum was similar to that published for patients with normal renal function. The dialyzability of amphotericin B was studied in vivo during a 6-h period of hemodialysis, by an in vitro dialysis of amphotericin B in water by using similar equipment, and a Pellicon membrane filter which retains molecular species of 100,000 molecular weight and higher. These studies revealed that the drug is not dialyzable with conventional hemodialysis membranes, regardless of protein binding in plasma, and is excluded from passing through the Pellicon membrane filter.