This interim analysis of the efficacy and safety of ciprofloxacin is based on case reports of 1241 adult patients treated primarily in the USA; 1026 were suitable for analysis of drug efficacy. The daily dose ranged from 500 to 1500 mg, the unit dose being given every 12 h. Duration of treatment ranged from 5 to 211 days (mean 12.6 days). In 1046 cases of infection the site was the urinary tract (514), skin structures (218), respiratory tract (215), blood (43), bone (27), abdomen (13), gastrointestinal tract (13) and pelvis (3). Organisms responsible for infection were Escherichia coli (282), Pseudomonas aeruginosa (238), Staphylococcus spp. (149), Streptococcus spp. (107), Klebsiella spp. (105), Proteus spp. (97), Haemophilus spp. (71), Enterobacter spp. (58), Salmonella spp. (44), Citrobacter spp. (27), and Serratia spp. (22). Signs and symptoms of infection resolved in 84% of all cases; 12.6% improved and 3.4% failed to improve. Pathogens were eradicated in 91% of urinary tract infections and in 87% of all other cases of infection combined; superinfections occurred in 5.3% of all patients. At the four-week follow-up 83% of patients with urinary tract infection still had sterile urine. Adverse reactions during therapy were considered probably or possibly drug-related in 166 patients. Nausea (37), diarrhea (25), vomiting (15), nervousness (28), and rash (9) were the most frequent; in only 2% of cases was it necessary to discontinue the drug. Results of ophthalmologic studies were generally unremarkable. Occasional elevations of SGOT and SGPT, and rare elevations of NPN related to ciprofloxacin therapy were seen.