Gatifloxacin is an 8-methoxy fluoroquinolone with broad activity against respiratory tract pathogens, including those commonly associated with community-acquired pneumonia (CAP). To evaluate the efficacy and safety of oral gatifloxacin 400 mg once daily for seven to 14 days, community-based physicians enrolled adult outpatients with confirmed or suspected CAP in a prospective, single-arm, open-label, noncomparative study. Of 1488 clinically evaluable patients with radiographically confirmed or clinically suspected CAP, 1417 (95.2%) were cured. All strains of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, the most commonly isolated pathogens, were susceptible to gatifloxacin. Penicillin nonsusceptibility was seen in 32.6% of S. pneumoniae isolates, and beta-lactamase production was detected in H. influenzae (26.9%) and M. catarrhalis (88%) isolates. Clinical cure rates of 91%, 94%, and 92% were achieved in patients with S. pneumoniae, H. influenzae, and M. catarrhalis, respectively. All seven patients with fully penicillin-resistant S. pneumoniae (MIC > or =2 micro g/ml) were cured. Gatifloxacin was well tolerated, with the most common drug-related adverse events being nausea (2.8%) and diarrhea (1.7%). Gatifloxacin is effective and well tolerated as empiric therapy for CAP in the outpatient community setting.