Current methods for testing stool samples for hemoglobin utilize peroxidase oxidation of chemical indicators such as guaiac or benzidine. These tests have frequent false-positive and false-negative results, complicating random screening for occult gastrointestinal bleeding. The authors have developed an immunochemical test for human blood in feces using goat antibodies to hemoglobin. When employed in radial immunoassay the test is uncomplicated by cross-reaction with common human foods or other nonhemorrhagic fecal fecal constitutents. The lower limit of sensitivity for hemoglobin in stool samples is 10 mg/dl, compared with a commonly reported threshold of 100 mg/dl for peroxidase tests. The test accurately detects hemoglobin in mixtures of human blood and feces. Immunochemical identification of human blood in stool offers improved detection of lower gastrointestinal bleeding.