Radioactive microspheres 15 µm in diameter were injected into the left ventricle of the heart of cats. Simultaneously a blood sample was drawn from the aorta. Standardized samples of the stomach wall were separated into mucosa and muscularis samples. For each sample the blood flow was calculated in terms of ml/minute/100 g tissue weight. The distribution of microspheres to different layers of the samples was determined microscopically. In the mucosa samples the majority of spheres were found in the propria and glandular layer, only a few percent in the submucosa. In the muscularis samples most of the microspheres were present in the muscle tissue, only l-9% in the submucosa fraction. The present method is considered to give a good expression of the capillary blood flow in the glandular layer of the mucosa and the muscularis.