Dirithromycin, a new once-daily macrolide, was studied in a multicentre, randomised, double-blind trial in community-acquired bacterial pneumonia. A total of 591 patients received either a single daily dose of dirithromycin, 500 mg, or erythromycin, 250 mg, four times daily. Clinical response rates were similar in both treatment groups (127 dirithromycin-treated and 118 erythromycin-treated patients): at the time of the final consultation, the clinical and bacteriological response rates for dirithromycin-treated patients were 94.5% and 93.0%, while for erythromycin-treated patients, they were 92.1% and 90.3%, respectively. The nature and frequency of treatment-emergent events were comparable. We conclude that dirithromycin, 500 mg, once daily, is safe and effective in the treatment of community-acquired bacterial pneumonia. The once daily dose is likely to improve compliance, making it preferable to erythromycin.