In an open study, a group of 11 patients with asymptomatic urinary tract infections, caused by resistant Pseudomonas strains, were given 200 mg of ciprofloxacin per day for 1 week. All strains displayed an in vitro sensitivity to the drug. Complete clinical resolution was obtained in 8 patients and long-term eradication in 3. No adverse reactions and only minor and reversible laboratory changes were recorded. Ciprofloxacin could be a valuable oral drug in the treatment of severe urinary infections. However, more clinical studies on the development of resistance under therapy and with other dose schedules are indicated.