The aim of the study was to evaluate whether a broad-spectrum penicillin, amoxicillin, was superior to placebo in resolving symptoms of acute exacerbations of chronic bronchitis in patients from general practice. 131 general practitioners included 278 patients over a period of 30 months. The patients were randomly assigned to treatment with amoxicillin 750 mg b.i.d. or corresponding placebo for 7 days. Patients with pneumonia, a temperature above 38.5 degrees C or heart rate over 100 were excluded for safety reasons. The main effect parameter--the doctors' overall evaluation of the treatment--did not demonstrate any statistically significant difference between amoxicillin or placebo, 63% versus 64% of the patients. Resolution of symptoms was obtained by 19% (25/132) of the patients in the amoxicillin group compared with 10% (13/136) of the patients in the placebo group, P = 0.03. The present findings do not favour routine use of antibiotics in an attempt to improve the course of acute exacerbations as defined in this study in patients with chronic bronchitis.