In a review of the US Bayer ciprofloxacin (CIP) database, an analysis was undertaken to summarize the effectiveness and tolerability of CIP 750 mg BID in the treatment of patients with acute exacerbations of chronic bronchitis (AECB) and pneumonia. In five controlled studies, comparator (COMP) agents included ampicillin, intravenous cefuroxime/cefaclor, and other unspecified agents. Primary efficacy end points were clinical success (resolution plus improvement) and bacteriologic eradication at the end of therapy. The incidence of adverse events for CIP 750 mg BID was compared with that for COMP and with that in the CIP 500-mg-BID AECB and pneumonia clinical trials database. In five uncontrolled studies, 443 patients received CIP 750 mg BID; in 5 controlled trials comprising 344 patients, 169 received CIP 750 mg BID and 175 received COMP. Clinical success for CIP was 93% (368/396) and 99% (160/162), respectively, in the uncontrolled and controlled studies versus 98% (156/160) for COMP agents. Corresponding bacteriologic eradication rates for CIP 750-mg-BID-treated patients were 77% (273/356) and 95% (122/128), respectively, and 77% (96/125) for COMP agents. Overall bacteriologic eradication by organism for CIP 750 mg BID included Streptococcus pneumoniae 96% (51/53), Haemophilus influenzae 98% (92/94), Haemophilus parainfluenzae 100% (56/56), Moraxella catarrhalis 100% (14/14; 13 of 14 organisms were isolated in patients with AECB), and Pseudomonas aeruginosa 66% (135/204). Drug-related adverse events were reported in 113 (26%) CIP 750-mg-BID-treated patients in uncontrolled trials and in 62 (37%) CIP 750-mg-BID- and 61 (35%) COMP-treated patients in controlled trials. In the combined data from the CIP 750-mg-BID uncontrolled and controlled trials, adverse events occurred with similar frequency compared with COMP except for nausea (CIP 10%, COMP 7%) and diarrhea (CIP 3%, COMP 13%). In conclusion, CIP 750 mg BID provided excellent clinical success rates in the treatment of patients with AECB and pneumonia. CIP 750 mg BID was well tolerated compared with the COMP agents administered.