The author studied the change of circulating eosinophils in mice inoculated with cancerous materials, and the following results were obtained. 1. The number of circulating eosinophils in mice decreased markedly four hours after injection of cancer tissue extract. 2. Urine (0.5cc) obtained from 15 out of 21 patients with gastric cancer decreased the number of circulating eosinophils in mice for over 50 per cent. 3. Same results were obtained from the urine of 2 out of 12 patients with gasttricduodenal ulcer and chronic gastritis.