Pan-Korean multi-center trial of doxycycline in the treatment of upper and lower respiratory infection was carried out in the summer(from May to October) of 1975. A total of 204 patients between the ages of 3 and 75 was treated by 37 physicians including the internal medicine, pediatrics and ENT specialist in 17 general hospitals and 2 private clinics all-over the country. The dosage recommended was 200 mg on the first day of therapy followed by 100 mg daily thereafter. The pediatric dosage was 4 mg/kg on the first day and then 2mg/kg on each successive day. The subjective and objective signs of respiratory infection such as temperature, cough, sputum, pain and associated inflammatory symptoms were assessed using the carefully designed protocols and it showed rapid improvement by the fifth day (80%) of therapy. Only minor side-effects were reported and these were mild and mainly limited to gastrointestinal tract. The overall evaluation of the trial showed that 170 patients(83.3%) had a very good or good result, 13 patients (6.4%) a moderate and another 13 patients (6.4%) a negative result.