Ofloxacin was used in the treatment of 15 patients (12 with pneumonia and 3 with aggravated chronic bronchitis). The drug was administered at first intravenously in a dose of 200 mg twice a day for 3 days and then orally in the same dosage. Before the treatment Streptococcus, Pneumococcus and Klebsiella strains were isolated from the sputum specimens (12, 2 and 2 cases respectively). All the isolates except for 3 Streptococcus strains were susceptible to ofloxacin. After the treatment the recovery and improvement were stated in 14 patients. One patient with pneumonia at the background of chronic bronchitis due to resistant Streptococcus strains was excluded from the trial since the treatment with ofloxacin failed. 252 isolates from the sputum specimens of the patients with pulmonary affections were subjected to the laboratory tests and high activity of the fluoroquinolone against the gram-positive and gram-negative organisms was shown. The isolates were often resistant to tetracycline. It was concluded that the use of ofloxacin in the successive therapy of patients with pulmonary diseases was expedient.