As an outgrowth of the investigators' description of the technique of angiographically demonstrating sites of gastrointestinal bleeding, as well as their control by intraarterial infusion of vasopressin, many questions have arisen regarding present techniques. The investigators are requesting renewal of their present grant to further refine and develop new approaches to this difficult and important problem. During the next three years, the investigators will attempt to evaluate resons for failure of transcatheter therapy to control bleeding in some patients. In addition, we will attempt to better define the role of angiography in the treatment of bleeding using a prospective randomized clinical study. The role of radioisotopes in the demonstration of bleeding sites will be investigated in the hopes of finding a relatively simple method of localizing acute hemorrhage. The efficacy of systemic vasopressin compared to intraarterial vasopressin in the treatment of arterial bleeding will be examined. Investigation will continue on colonic angiodysplasia concerning the histologic nature, relative frequency and etiology of this lesion. An attempt will be made to determine the safety of long term infusions of vasopressin in the hepatic artery. The role of contraction of the wall of the esophagus, stomach and bowel in the control of bleeding will be examined.