A total of 30 hospitalized patients with upper and lower urinary tract infections were treated with cefotaxime (HR-756) by intramuscular or intravenous route. All patients had a monomicrobial infection, and the major part of bacterial isolates were gram-negative bacilli (83%) while gram-positive cocci accounted only for 17%. In 83% of the cefotaxime-treated patients both the bacteria and symptoms were eliminated at the 2nd week of follow-up, while failure or relapse occurred in 17% of the patients. No reinfections were recorded. Cefotaxime was a safe and well-tolerated drug and can be considered as an effective antibiotic in the therapy of urinary tract infections caused by "difficult' gram-negative bacilli.