The efficacy of amphotericin B bladder irrigation at two concentrations was studied. Patients with funguria (> or =15,000 colony-forming units of yeast per milliliter of urine), an indwelling urinary catheter, and a physician order for amphotericin B continuous bladder irrigation were randomly assigned to receive 10 or 50 mg of amphotericin B per liter of sterile water as a continuous irrigation for 72 hours at the rate of 42 mL/hr. Before the bladder irrigation began, the indwelling catheter was changed to a three-way catheter. Repeat urine cultures were performed 24 hours after the irrigation was discontinued. A total of 28 patients were enrolled from November 1993 to May 1995. The rate of eradication of the infection was 100% in the 50-mg/L group and 67% in the 10-mg/ L group. Subject enrollment was stopped prematurely because all the treatment failures occurred in the 10-mg/L group. Dose was the only variable significantly associated with outcome. Bladder irrigation with amphotericin B was more effective when the drug concentration was 50 mg/L rather than 10 mg/L.