This study examines the frequency of upper GI bleeding in the United States population, and the use of diagnostic endoscopy in its evaluation. Data from the National Hospital Discharge Survey and National Ambulatory Medical Care Survey are used, as well as limited data from the Veteran's Administration and State of Wisconsin. There were almost 1.1 million discharges from U.S. hospitals in 1978 with diagnoses related to UGI bleeding. Using an indirect method of estimation based on cases of peptic ulcer specified as bleeding, we estimate the rate of hospitalization with UGI bleeding as 150 per 100,000 population per year. About one-sixth of these patients underwent gastroscopy and/or esophagoscopy in 1978, approximately a three-fold increase over five years previously. National mortality from UGI bleeding decreased approximately 40 percent between 1968 and 1977, but data are inadequate to infer a relationship to increased use of endoscopy. Suggestions for further research are specified.