The present study compares the clinical efficacy and side-effects of amoxycillin in two groups of children at the age of six years or less randomly assigned to amoxycillin therapy 40 mg/kg/day either two or three times daily for the clinical diagnosis of acute respiratory tract infections. Both treatment groups were comparable according to age, sex, weight and additional treatment. Acute otitis media occurred in 152 out of 187 (81%) patients receiving amoxycillin three times daily, and in 153 out of 180 (85%) patients with a twice daily dosage schedule. A clinical diagnosis of acute bronchitis was made in 55 cases (29%) in the former group and in 59 cases (33%) in the latter group. In the patient group with twice daily dosage schedule, 82% of the patients with otitis media were cured. The corresponding figure in the thrice daily group was 86%. On the basis of the disappearance of the symptoms and the improvement of the signs the overall results are equally good in both treatment groups. The number of side-effects of amoxycillin was equal in both groups, 6.4% and 6.7% respectively. Exanthem was the most frequent side-effect. No serious side-effects occurred. Our results indicate that the same total daily dose of amoxycillin given either three times daily or two times daily is comparably effective and tolerated in children with acute respiratory infections, e.g. acute otitis media and acute bronchitis.