The feeding response to cold exposure of male Sprague-Dawley rats bearing Walker 256 carcinosarcoma has been measured at 5 degrees, 13 degrees, and 17 degrees exposure. The cold-specific feeding response of the host is estimated taking account of the food cost of the tumor and of changes in food intake induced by weight change of host produced by both cold exposure and tumor growth. The cold-specific feeding response to cold exposure is depressed by about 30% by presence of tumor but is only marginally influenced by tumor size. This tumor-induced impairment of feeding response contrasts with the eventual total abolition and tumor size dependency of feeding response of tumour bearers to caloric density of food.