Patients with lower respiratory tract infections [pneumonia (n = 16), bronchiectasis (n = 5) and acute exacerbations of chronic bronchitis (n = 44)] were treated daily with amoxycillin/clavulanic acid given either 1.2 g intravenously three times daily or 625 mg orally three times daily for 7-15 days. Symptoms, signs and sputum volume and colour were monitored daily. Chest X-ray, sputum culture and Gram-stain examinations were also carried out on days 1 and 5, and immediately after the end of the treatment. There was a clinical improvement, as indicated by the incidence of cough, dyspnoea and rales, and by sputum volume and colour in 90.8% of the patients. Microbiological improvement, as indicated by the complete elimination of sputum pathogens and pus cells, was achieved in the same proportion of patients (90.8%). In one patient, an adverse side-effect, diffuse exanthema, was noted. Amoxycillin/clavulanic acid possesses a high clinical and microbiological efficacy for lower respiratory tract infections.