In order to evaluate the efficacy, safety and usefulness of pipemidic acid (PPA) in complicated urinary-tract infections, a controlled study using carindacillin (I-CBPC) as a reference standard drug was carried out by a double blind method in collaboration with 48 clinics throughout the country. From the results obtained, the following conclusions were drawn.<BR>1. In total of 586 patients, 55 cases were excluded, 38 cases dropped out and 493 cases which consisted of 249 cases given PPA and 244 cases given I-CBPC.<BR>2. For the background characteristics, there were no statistically significant differences between PPA and I-CBPC, indicating that comparison between these drugs was meaningful.<BR>3. The daily dose for both PPA and I-CBPC was 2g each and medication was continued for 7 days.<BR>As to the overall clinical efficacy, the rate of “excellent” response was found to be 21.3% with PPA and 16.0% with I-CBPC without significant difference between the two groups. The rate of both “excellent” and “good” response was 54.2% with PPA and 35.7% with I-CBPC and the former was significantly higher than the latter.<BR>4. The rate of efficacy on pyuria was found to be 34.1% with PPA and 24.2% with I-CBPC in respect to “cleard” response and 49.8% with PPA and 37.7% with I-CBPC in respect to both “cleared” and “decreased” responses. The rates of PPA were significantly higher than those of I-CBPC.<BR>5. The rate of efficacy on bacteriuria was found to be 43.4% with PPA and 25.4% with I-CBPC in respect to “eliminated” response and 47.0% with PPA and 29.1% with I-CBPC in respect to both “eliminated” and “suppressed” responses. The rates of PPA were also significantly higer than those of I-CBPC.<BR>6. When stratified according to the rate of, infection, it was remarkable that the effective rate of PPA on the prostatic bed infection was significantly higher than that of I-CBPC.<BR>When analyzed according to the type of infection classified by UTI-Committee, the rates of efficacy of PPA on all types of infection except type I and V were more than 50%. In even type I and V, the drop of the rate of efficacy of PPA was less than that of I-CBPC.<BR>The results indicated that PPA was expected to be more or less effective on all types of complicated urinary-tract infections.<BR>7. PPA eliminated more than 40% of causative organisms, suggesting that it might be effective on any organism inducing complicated urinary-tract infections.<BR>It was remarkable that the eradication ratio of PPA for E. coli, indole negative and positive Proteus, and Citrobacter were more than 90%.<BR>No significant difference between PPA and I-CBPC was shown in the rate of disappearance of Pseudomonas.<BR>8. In the global judgement made by attending physicians, the rates of efficacy and usefulness of PPA were significantly higher than those of I-CBPC.<BR>9. Incidence of side effect was 9.4% and 7.6% in PPA and I-CBPC respectively without significant difference between them.<BR>As side effects, symptoms were mainly gastric disturbances with a few allergic responses.<BR>Neither PPA nor I-CBPC showed serious side effect.<BR>From the above results, PPA would be a useful drug for the treatment of complicated urinary-tract infections, which may be applied broadly.