The purpose of this work was to evaluate, in a selected group of massively bleeding ulcer patients, the prognostic significance of a series of easily recognizable factors, all of which have been ascribed a decisive importance. These factors were: Complicating diseases, passage of red or chemically changed black blood, age and sex of the patients, and site of the ulcer, whether in the stomach or duodenum. Thereally important factorsconveyinga poor prognosis were found to be: presence of complicating diseases and passage of red blood orally or per rectum. Age and sex of the patients and site of the ulcer were factors of only apparent importance. Any difference in mortality between subgroups of patients separated after these criteria was explained by unequal distribution of patients with complicating diseases and red haemorrhage. No evidence was found for the belief that elderly patients bleed more severely than younger patients.