Comparative efficacy of lomefloxacin (400 mg daily for 5 days) and roxithromycin (150 mg daily for 5 days) was studied in the treatment of 24 patients (12 males and 12 females) at the age of 39 to 83 years (the average age of 59 years) with exacerbation of chronic obstructive bronchitis. The efficacy was estimated by the clinical data and the results of the bacteriological analysis of the sputum. The drugs were shown to be equivalent in their clinical and microbiological efficacies. The use of the drugs should be based on the results of the sputum bacteriological analysis and the pathogen susceptibility tests. The tolerance of roxithromycin and lomefloxacin was good. No significant adverse events were recorded.