Recent studies on bacteriological findings in chronic maxillary sinusitis show a great variety of aerobic as well as anaerobic germs. For these reasons adequate chemotherapy has to support the necessary surgical procedure. In this study, the author reports about 60 adult patients suffering from chronic maxillary sinusitis. All of them had to undergo surgical treatment by the Caldwell-Luc procedure. Postoperatively, 30 of them were treated with brodimoprim, the others with doxysycline for 7 days. Bacteriological investigations have been performed during and at several days after surgery. At the same time, a number of laboratory data and the complications observed were registered. In this way, a comparative study of the two antibiotic drugs concerning the therapy of chronic maxillary sinusitis was established.