Gatifloxacin is an advanced-generation fluoroquinolone with demonstrated efficacy and safety as therapy for community-acquired pneumonia (CAP). As part of a phase IV postmarketing surveillance program (TeqCES), 136 outpatients with CAP whose sputum was culture-positive for Streptococcus pneumoniae were enrolled in an open-label trial of oral gatifloxacin 400 mg daily for 7 to 14 days. An antibiogram of isolates showed 100% susceptibility to gatifloxacin (MIC(90) 0.5 micro g/mL) and respective susceptibilities of 67%, 70%, and 80% to penicillin, erythromycin, and tetracycline. Clinical cure was achieved in 95.3% of evaluable patients, including seven patients infected with penicillin-resistant S. pneumoniae (MIC > or =2 micro g/mL). The bacteriologic eradication rate for S. pneumoniae was 94.5%. Diarrhea, nausea, and dizziness, the most common adverse events in CAP patients (<3%), were generally mild to moderate; no serious adverse events were recorded. These results support recommendations to treat CAP, particularly due to S. pneumoniae including multidrug-resistant strains, with the newer 8-methoxy-fluoroquinolone, gatifloxacin.