With the purpose of assessing whether the effect of a drug at an early stage of administration could serve to predict efficacy at the end of drug treatment, a cephem antibiotic was administered for 5 days (days 0-4) by injection in males with complicated UTI. Results showed that the bacteriological effect on day 1 was reflected in the overall clinical efficacy on day 5. The activity of an antibacterial agent appeared to be reflected in the ability to eliminate bacteria 1 to 2 days after the start of drug administration.