Flucytosine (5-FC), an oral antifungal agent, was used in the treatment of 37 patients with urinary tract infections due to fungi. Criteria for treatment included pyuria of greater than or equal to 5 WBCs/HPF, fungal colony counts in urine greater than 10(3) CFU/ml and the presence of candiduria in 2 consecutive urine culture with interval of 7 days. Patients received 2 approximately 8 g/day of 5-FC for 7 to 14 days. The clinical efficacy was evaluated in 27 patients with 14 day-treatment and overall efficacy rate was 77.8%. In patients with indwelling catheter, overall efficacy rate was lower than that in patients without catheter. Twenty-two of 30 strains (73.3%) were eradicated by the treatment. The MIC of 5-FC for isolates was less than 0.78 micrograms/ml except for 5 strains. The secondary resistance during 5-FC treatment was observed in early phase in 6 patients whose clinical efficacy was poor. The loss of appetite and mild leukocytopenia were observed as adverse effects. From the results of our study, 5-FC appears to be effective and safe in the treatment of urinary tract infection due to fungi.