The importance of the different endoscopic procedures in the transmission of hepatitis B was investigated prospectively by following up for 6 months all HBV-negative patients endoscoped from April to October 1981. A group of patients admitted in the same period to our unit constituted the control group. Controls were obtained after 1, 3, and 6 months from endoscopy. Infection rate was 1% for the control group and 0.45% for the endoscopy group. The difference is not statistically significant. These results strongly support the view, already present on an uncontrolled basis in the literature, that transmission of hepatitis B is not associated with gastrointestinal endoscopy.