During the clinical development of ciprofloxacin 1,519 treatments of UTI were documented. The most frequent specific diagnoses were uncomplicated UTI (46.6%), followed by non-specified UTI (21.7%), complicated UTI (19.4%), acute pyelonephritis (7.6%) and chronic pyelonephritis (4.1%). 70% of the causative organisms isolated were Enterobacteriaceae (Escherichia coli 38%, Proteus spp. 10% and Klebsiella pneumoniae 10%). Pseudomonas aeruginosa occurred in approximately 20% of the cases and the remaining 10% were gram-positive aerobes. Clinical resolution was achieved in about 90% in all specific diagnoses. The eradication rate for gram-negative Enterobacteriaceae was 93.8%, for P. aeruginosa 81.8% and for gram-positive aerobes 90.2%. Studies comparing ciprofloxacin and standard treatment have shown the high efficacy of ciprofloxacin making it a preferred agent particularly for infections caused by pathogens less susceptible to conventional drugs. According to the experience of clinical trials the recommended ciprofloxacin dose varies between 100 and 500 mg b.i.d. orally depending on the severity of clinical status and the susceptibility of the pathogen.