The prophylactic and chemotherapeutic efficacy of PMPC against infections after TUR-P has been investigated. Bacteriological evaluation: PMPC , 200-300 mg/day for 2-12 weeks, was administered to 49 patients, who had over 10(3)CFU/ml of microorganisms after CET or CEC treatment for 3-7 days. The eradication rate of microorganisms was 40.8% after 2 weeks, 52.2% after 4 weeks, 64.1% after 6 weeks, 65.0% after 8 weeks and 70.6% after 12 weeks. Effectiveness on pyuria : The improvement rate of pyuria against 59 patients who had over 10(5)/hpf of pyuria , was 15.3% after 2 weeks, 16.4% after 4 weeks, 25.4% after 6 weeks, 58.5% after 8 weeks, 72.7% after 10 weeks and 75.0% after 12 weeks. Overall clinical efficacy on PMPC was examined in 26 patients. The results of efficacy were 27.3% after 2 weeks, 48.0% after 4 weeks, 50.0% after 6 weeks, 69.2% after 8 weeks, 75.0% after 10 weeks and 77.0% after 12 weeks. The clinical response was evaluated according to a criterion for clinical evaluation of antimicrobial agent on chronic complicated UTI proposed by UTI committee in Japan. No severe adverse effect including allergic reaction was found. Following administration of PMPC , three patients experienced adverse gastric reactions, and drug administration was discontinued at week 6 or 8. PMPC was effective as a prophylactic chemotherapeutic drug against infections after TUR-P and prostatectomy.