Examinations of occult blood in feces were performed after a certain amount of blood treated previously with hydrochloric acid limonnde was given into the stomach or duodenum through a Levin tube. The follwing results were obtained. 1. All the cases were positive in the reaction after the administration of more than 2 ml. of the blood. 2. No significant difference in the reaction between intragastric and intraduodenal administration. 3. The intensity of the positive reaction became weak as the acidity in gastric juice became high. 4. The longevity of the positive reaction was prolonged with larger amount of the blood given but they were not proportional when the amount of more than 3 ml. of the blood was administrated. After 4 days all the cases showed negative reaction.