Food intake of parabiotic rats was studied for at least 24 days by using partitioned cages. After hypothalamic lesions were placed in one rat, the daily food intake of its normal partner remained at the same preoperative level. In control pairs, starvation of one rat did not cause the daily food intake to increase in the other rat. These findings, along with data from a pair with cross anastomosis of small intestines, clearly indicate that humoral signals for inhibiting and facilitating feeding, if they do exist, cannot be transferred readily through the parabiotic union. Other experiments showed that the parabiotic preparation can be used to study the regulation of water intake.