A double-blind comparative clinical trial of doxycycline (200 mg on the first day followed by 100 mg daily for a total of 7 days) and ampicillin (250 mg 4 times daily for 7 days) was performed in 44 patients with acute or chonic sinusitis. Significantly superior results were observed with doxycycline; 90% of the patients responded to doxycycline and 35% to ampicillin. The incidence of side-effects was low and these were of a minor nature, in no case with either drug was discontinuance of treatment necessary. These results imply that in treating chronic bronchitis an antibiotic should be given which is effective not only against the responsible organisms but which is able also to penetrate those tissues (such as the sinuses) that act as a reservoir for these organisms. Doxycycline meets these requirements.