Ofloxacin and amoxicillin in the treatment of 121 bronchopulmonary infections were compared in a randomized, open clinical trial. 64% of the infections were pneumonias. S. pneumoniae, H. influenzae and B. catarrhalis accounted for 76% of the etiologic agents. The clinical and bacteriological responses were positive in more than 90% of the patients and comparable in both groups. None of the isolated agents was resistant to ofloxacin, whereas 21% were amoxicillin-resistant. Ofloxacin was used without randomization in the treatment of 26 atypical pneumonias and opportunistic infections, all of which were cured or improved. Occurrence of side-effects was rarely observed in either treatment group.