With regard to the changing resistance of microorganisms it is important to develop and test steadily new chemotherapeutic agents. The authors used the preparation CIPROBAY of Bayer Co. (ciprofloxacin) prophylactically in 60 patients of a group before instrumental endoscopic examination of before endoscopic operation. Evaluation of the results of Ciprobay administration revealed a high antibacterial and very good tolerance and simple administration of the preparation.