Candidiasis often is the final insult to the critically ill patient. Flucytosine, an orally administered antifungal agent, was used in the treatment of 225 patients with genitourinary candidiasis. Criteria for treatment included clinical manifestations, high urine colony counts of Candida, serologic findings and in vitro sensitivity of Candida to flucytosine. Infection was eradicated in 212 patients (94 per cent), as determined by clinical and laboratory criteria. The only significant adverse drug effect was reversible agranulocytosis, which ccurred in 2 patients. Thirteen patients (6 per cent) required supplemental therapy with systemic or bladder irrigations of amphotericin B.