An open study was conducted in 40 randomized patients to evaluate the efficacy of ofloxacin in comparison with cefazolin in the treatment of acute, chronic and recurrent lower respiratory tract infections. The therapeutic efficacy of the two drugs was evaluated on the basis of bacteriological and clinical examinations. Bacteriological assays revealed that ofloxacin eliminated bacterial flora from sputum in 20/21 cases (14 Gram-negative and 7 Gram-positive), while cefazolin eradicated the pathogens in 12/19 cases (16 Gram-negative and 3 Gram-positive). In clinical terms, 20/21 (95.2%) infections were cured and 1/21 (4.8%) improved in the ofloxacin group as against 12/19 (63.2%) cured, 5/19 (26.3%) improved and 2/19 (10.5%) unchanged in the cefazolin group. The results of this study confirm the efficacy and excellent tolerance of ofloxacin in the treatment of lower respiratory tract infections.