The clinical efficacy and tolerability of ciprofloxacin (Bay o 9867), a new quinolone compound with broad antibacterial spectrum, was evaluated in 28 patients hospitalized in the first Clinic of Infectious Diseases, University of Naples, Italy, for chronic liver disease and affected by respiratory (RTI) or urinary tract infections (UTI). Ciprofloxacin was administered at the dosage of 500 mg twice a day after the isolation of the organism responsible for the infection and after the determination of its sensitivity in vitro to ciprofloxacin. The therapy was carried on for 5-10 days depending upon the severity of infection and clinical evaluation. Bacteriological cultures and hematochemical analysis were always performed during and after the therapy. Ciprofloxacin was very effective in all the treatments of UTI and RTI under examination, both for the disappearance or improvement of clinical signs and for eradication of the responsible microorganisms. No significant side effects or change in the hematochemical tests were observed.