The efficacy of ciprofloxacin was studied in the treatment of 22 patients with hospital infection of the lower respiratory tract: 10 patients with nosocomial pneumonia, 8 with exacerbation of chronic obstructive bronchitis, 3 with exacerbation of mucoviscidosis and 1 with bronchiectasis. The drug was administered intravenously in a dose of 200 to 400 mg or orally in a dose of 500 to 750 mg twice a day for 6 to 21 days. The clinical and bacteriological efficacies of ciprofloxacin amounted to 90.9 and 86.4 per cent respectively. The treatment failed in 2 patients: 1 with pneumonia due to Streptococcus pneumoniae and 1 with mucoviscidosis and persistence of Pseudomonas aeruginosa. Ciprofloxacin was well tolerated. The side effects were observed in 2 patients and required no discontinuation of the drug use.