The clinical efficacy of the combination therapy with cefmenoxime plus cefsulodin was studied in patients with complicated urinary tract infections caused by Pseudomonas aeruginosa. Patients received 1 g of CMX and 1 g of CFS concomitantly twice a day by 1-hour intravenous drip infusion. Of a total of 127 patients who received medication, 82 patients were evaluated on the 5th day. The overall clinical efficacy of treatment was evaluated by the criteria proposed by the UTI Committee, Japan, as excellent, moderate or poor. It was excellent in 15%, moderate in 55% and poor in 30%. Of the 143 strains isolated from 82 patients, 115 strains (80%) were eradicated. The eradication rate of P. aeruginosa was 83%. Subjective side effects were observed in 3 (2.4%) of the patients. Drug-related aggravations in laboratory test results were observed in 8 (7.5%), but most of them were minimal and reversible. The results of this study suggest that a combination of cefmenoxime and cefsulodin might be useful in the treatment of complicated urinary tract infections caused by P. aeruginosa.