Brodimoprim was studied in the treatment of acute respiratory tract infections in hospitalized, basically healthy, military conscripts. Its efficacy and tolerance were compared to those of doxycycline in a clinical randomized double-blind trial. 60 pts. were divided into two equally large groups. One group received brodimoprim, 400 mg as a loading dose followed by 200 mg daily, for 10 days. The other group received doxycycline, 200 mg as a loading dose followed by 100 mg daily, for 10 days. In the brodimoprim group, 23 patients (77%) were cured, 5 patients (16%) improved and 2 patients (6%) were considered failures. In the doxycycline group, 26 patients (87%) were cured, 3 patients (10%) improved and 1 patient (3 9%) did not respond. The only side effect in the whole study was moderate diarrhea in 1 patient in the brodimoprim group. Clinically and according to the normalization of laboratory values, the two drugs tested were equally effective.