We clinically evaluated the usefulness of a new oral antimicrobial agent, TFLX, in the field of urology. The dose administered was 150 mg t.i.d and the duration of administration was 3 days. The clinical effect was evaluated according to the criteria of the Japanese UTI committee. The clinical response obtained on 164 female patients with acute simple cystitis was excellent in 118, moderate in 44 and poor in 2 patients. The efficacy rate was 98.78%. The clinical response obtained on 4 male patients with acute simple cystitis was excellent in 2 and moderate in 2 patients. The efficacy rate was 100%. The clinical response obtained on 3 female patients with simple pyelonephritis was excellent in 2 and moderate in 1 patient. The efficacy rate was 100%. The clinical response obtained on one patient with non-gonococcal urethritis was excellent by doctor's evaluation. The clinical response obtained on 7 patients with complicated UTI was excellent in 3 and moderate in 4 patients. The efficacy rate was 100%. Three patients complained of stomach distress or malaise and 2 patients developed rash. No abnormal laboratory data were observed. Thus, TFLX appears to be safe and suitable for use in the field of urology.