To determine the risk of bacteremia, 53 patients had blood collected for culture before and five, ten and 15 minutes following fiberoptic endoscopy of the upper digestive tract. One patient had transient bacteremia with Acinetobacter Sp. five minutes after endoscopy. Combining our study with four others, 447 patients have been evaluated of which 6% had bacteremia after upper gastrointestinal endoscopy. Biopsy or other endoscopic operation does not increase the likelihood of bacteremia. We recommend careful attention to instrument and accessory cleaning and prophylactic antibiotics (probably penicillin or oxacillin alone suffices) only for patients with prosthetic heart valves.