The postoperative duration of pyuria was studied in 35 patients who underwent transurethral resection of the prostate (TUR-P). The average postoperative duration of pyuria was 58.0 +/- 23.6 days. The age over 70 years, preoperative indwelling of urethral catheter and the preoperative urinary tract infection did not make the duration of pyuria longer. The volume of resected prostatic tissue over 20 g and the existence of diabetes mellitus make it significantly longer. It is effective and safe to use a low-dose antibacterial agent such as NFLX which has a broad spectrum and hardly develops bacterial resistance after TUR-P. It is suggested unnecessary to change the anti-bacterial agent even when pyuria continues.