Cefuroxime axetil 250 mg twice daily and amoxycillin 250 mg three times daily were compared in an investigator-blind, randomised, parallel group, multicentre study of acute or acute-on-chronic bronchitis. The two compounds had broadly similar efficacy. Analysis of patients on an intention-to-treat basis 24-72 hours after completion of the course of study medication showed that amoxycillin afforded clinical cure or improvement in 123/153 (80.4%) of patients and cefuroxime axetil in 109/143 (76.2%). This result was not significantly different, but the amoxycillin cure rate was not sustained and there were significantly more clinical relapses during the 4-week follow-up period following the end of treatment. Only 4/68 (5.9%) of patients receiving cefuroxime axetil relapsed and required further treatment, whereas 16/77 (20.8%) of those receiving amoxycillin needed further treatment (P = 0.016). These were all patients who had initially responded to treatment and had been adjudged clinically cured or improved. The significant difference in relapse rates suggests that the apparent clinical success with amoxycillin was not sustained. There were no differences between the two treatments in the numbers of patients experiencing adverse events, which were generally mild and transient.