Flucytosine is effective in the treatment of serious fungal infections. Some of the patients might have acute renal failure requiring continuous hemofiltration as renal replacement therapy. We evaluated the removal of flucytosine in a patient who received the drug for systemic Candida infection while undergoing continuous hemofiltration for acute renal failure. Arterial, venous, and ultrafiltrate sample pairs were collected to evaluate flucytosine removal. Ultrafiltrate/arterial drug concentration ratios and sieving coefficients obtained with the polysulfone membrane were higher than those obtained with the polyacrylonitrile membrane. Between 2.54 and 22.56 mg of flucytosine was removed from the patient per hour when the serum drug concentrations were 21.1-126.5 mg/l. The amount of hemofiltration flucytosine removal was related to ultrafiltration flow rate, serum drug concentration, and hemofilter type. The mean continuous arteriovenous hemofiltration flucytosine clearance for the polysulfone membrane was 77.0 +/- (SD) 15.6% of the ultrafiltrate flow rate, while the clearance for the polyacrylonitrile membrane was 51.0 +/- (SD) 5.7%. In patients with renal failure, continuous hemofiltration can remove an appreciable quantity of flucytosine when the ultrafiltrate flow rate is high. Serum drug concentration determination is necessary to devise an optimal dosage regimen for the patient.