This study aimed at determining the clinical efficacy and clinical and biological safety of ofloxacin compared to amoxicillin. 44 patients were included, and 41 were evaluable. 33 patients were treated according to the randomization list, whereas 11 patients were treated in an open study. All patients were suffering from acute, recurrent or chronic, lower respiratory tract infections. 29 patients started ofloxacin treatment with a dosage of 200 mg or 300 mg b.i.d., and 15 other patients received 1 g amoxicillin b.i.d. or t.i.d. Three patients of this last group were treated with ofloxacin after amoxicillin treatment failure. Bacteriological eradication was achieved in 95% of ofloxacin-treated and in 78% of amoxicillin-treated patients. Clinical cure occurred in 86% of ofloxacin- and in 55% of amoxicillin-treated patients. Successful treatment (bacteriologic eradication associated with clinical cure) was observed in 75% of patients from the ofloxacin-group and in 36% of the amoxicillin-group. No clinical adverse reactions were seen in amoxicillin-treated patients, whereas one patient in the ofloxacin-group was complaining of mild, definitely drug-related, hypochondrial pain. No major drug-related disturbances of biological parameters were observed neither in the ofloxacin- nor in the amoxicillin-group.