Gastric blood flow and its intramural distribution were studied in anesthetized cat and man by recording the elimination of intra-arterially injected krypton-85. The elimination was monitored with two external detectors--a scintillation detector recording the disappearance of gamma-activity from the entire gastric wall and a G-M tube recording the disappearance of beta-activity from the muscle layer only. Total and muscle layer blood flow could be calculated from the washout curves, and, knowing these variables, the blood flow to the mucosa-submucosa could be indirectly calculated. Gastric blood flow in the cat and man closely resembled each other, both in magnitude and distribution. Total blood flow in man 'at rest' was 12 +/- 4 ml/min and 100 g tissue (mean +/- S.D.; no. = 20), muscle blood flow amounting to 7 +/- 3 and mucosa-submucosa flow to 16 +/- 8 ml/min and 100 g muscle and mucosa-submucosa tissue, respectively. The distribution to the muscle layer was 26 +/- 14% and to the mucosa-submucosa 74 +/- 14% of total gastric blood flow.