Intravenous ciprofloxacin at a daily dosage of 400 mg divided in two doses was administered to 19 patients with severe infections caused by ciprofloxacin-susceptible bacteria. These infections included: 11 surgical would infections, 5 soft tissue infections, 2 respiratory tract infections, 1 urinary tract infection. The offending pathogens were: 8 coagulase-negative staphylococci, 3 Staphylococcus aureus, 3 Pseudomonas aeruginosa, 2 Proteus spp., 1 Escherichia coli, 1 Branhamella catarrhalis, 1 Klebsiella ozenae and 1 Serratia liquefaciens. Overall, 17 of 19 infections (89%) showed a satisfactory clinical response to trial therapy (15 cures and 2 improvements). Microbiological eradication was observed in 17 out of 20 isolated pathogens. Emergence of resistance to ciprofloxacin occurred in 1 coagulase-negative Staphylococcus and was associated with clinical failure. No side effects were observed. We conclude that intravenous ciprofloxacin may represent efficacious and safe therapy of severe infections; however close microbiological monitoring seems to be necessary to evaluate the emergence of resistance during quinolone therapy.