The efficacy and safety of oral ofloxacin, 400 mg once daily, for the treatment of patients with lower respiratory tract infections were studied. The most common species recovered from the sputum specimens of these patients were Haemophilus influenzae, followed by Streptococcus pneumoniae (S. pneumoniae), Staphylococcus aureus (S. aureus), Gram positive cocci unidentified, Pseudomonas aeruginosa (P. aeruginosa), Morexella catarrhalis, Streptococcus epidermidis, and another Haemophilus species in this order. All these bacteria were susceptible to ofloxacin except for one strain of methicillin resistant S. aureus. A satisfactory clinical outcome was achieved in 34 of 40 patients (85%). It is concluded that ofloxacin, 400 mg once daily, is useful for patients with respiratory tract infections.