We have evaluated the clinical effectiveness and possible side effects of oral ciprofloxacin therapy in 24 patients (11 females and 13 males). Two episodes from overall 25 infections were excluded of clinical and microbiological evaluation but were assessed regarding possible side effects. In most patients, the clinical condition was stable at the beginning of therapy. Only 3 patients had nonfatal diseases. Seventeen episodes were urinary tract infections (four of them with concomitant bacteremia), four chronic osteomyelitis, and two severe soft tissue infections; 21 episodes were monomicrobial, and two polymicrobial. The isolated organisms were mostly aerobic gram negative bacilli or facultative anaerobes: E. coli (9), Pseudomonas aeruginosa (5), Proteus mirabilis (5), Serratia marcescens (1), Klebsiella pneumoniae (1), Pseudomonas stutzeri (1), and Acinetobacter calcoaceticus (1). There were only two gram positive isolates: Staphylococcus aureus (1) and Staphylococcus epidermidis (1). The overall clinical response rate was 91%. Gastrointestinal tolerance was excellent. Colonization by Candida or Enterococcus developed in 3 cases (13%), and only one of them developed superinfection. Four patients developed several nervous system abnormalities, two increased transaminase activity and one drug exanthema. Ciprofloxacin appears as an effective drug for the monotherapy of several bacterial infections, including severe enterobacteriaceae and Pseudomonas infections.