In order to determine the efficacy and safety of the new quinolone ofloxacin in the treatment of chronic lower respiratory disease, 674 patients (353 with chronic bronchitis, 212 with community-acquired pneumonia and 109 with hospital-acquired pneumonia) were treated with ofloxacin 200 mg twice a day. In total, 627 patients (93%) showed a satisfactory clinical response, and 47 patients (7%) had no change or deterioration. Neither severe side effects nor interactions between ofloxacin and coadministered theophylline were seen. This is important in patients suffering from chronic obstructive airways disease. The antibiotic spectrum of ofloxacin covers nearly all bacterial pathogens causing infectious respiratory disease; furthermore, ofloxacin reaches high concentrations in pulmonary secretions and tissue. Ofloxacin is a proven antibiotic substance useful in the treatment of lower respiratory tract infections.