A prospective study was undertaken to investigate the frequency of bacteremia after endoscopy of the gastrointestinal tract. In one out of 100 patients undergoing gastroscopy and in one out of 25 patients undergoing coloscopy, positive blood cultures could be demonstrated. In both cases anaerobe lactobacilli were recovered. No bacteremia was demonstrated in 25 patients undergoing endoscopic retrograde cholangiopancreatography (ERCP).