This study was undertaken to evaluate the efficacy of a fixed combination of amoxicillin and clavulanic acid in 33 patients with chronic or recurrent respiratory tract infections (R.T.I.), mainly bronchitis. In two patients bronchopneumonia was diagnosed, and in one cystic fibrosis. The patients were treated with 750 mg of the drug combination (500 mg amoxicillin/250 mg clavulanic acid) t. i. d. for seven or ten days. Good clinical success was obtained in 17 patients and a clear improvement in another eight. The most frequently isolated micro-organism was Haemophilus influenzae; of the 22 strains isolated, 20 were resistant to 2 mg/l amoxicillin but sensitive to the combination of 2 mg/l amoxicillin and 1 mg/l clavulanic acid. Side-effects were reported in nine patients; two patients discontinued treatment for this reason. Amoxicillin/clavulanic acid is a useful therapeutic addition to the existing forms of treatment for amoxicillin-resistant respiratory tract infections.