METHODS Bilateral electrolytic lesions were producedin the different areas of the hypothalamus of sixteen cats and seventeen monkeys (macacu. s), with the aid of the Horsley-Clarke stereotaxic instrument. Only those animals which recovered consciousness after operation and became awake and active are being reported here. Those that remained somnolent are reported elsewhere. The cats weighed between 2-5 and 4 kg, and the monkeys between3-5 and 4-5 kg. Intraperitonealpentobarbitone sodium (M. & B.) was used for anaesthesia (0-7-0-8 ml. of a 5% solution/kg body weight in monkey and 0-8-1 ml. in cat). Intraperitoneal Dial (Ciba) was tried for anaesthesia at first but was discarded as the animals did not recover consciousness for 2-3 days. Withpentobarbitone, they recovered consciousness within a few hours after the operation. With the head in the stereotaxic instrument, a small craniotomy was performed, and lesions were produced witha unipolar electrode directed into the hypothalamus. An indifferent electrodeapplied on the surface of the animal served as an earth. At each point in the hypothalamus, electrolysis was produced by passing a direct current of 3 mA for 30 sec. Lesions of any size can be produced by electrolysis at adjacent points, separated from each other by lf-2 mm. The co-ordinates of the stereotaxic instrument for different regions of the hypothalamus bothin cats and monkeys had been worked out previously. These animals were fed ad lib., both before and after the production of hypothalamic lesions. A daily record was kept of food intake and weight. The cats were fed on minced meat and milk, and the monkeys on nuts, fresh fruit and vegetables. The animals that developed aphagia were kept alive by feeding on milk and egg mixture by stomach pump, with no tube feeding on certain days to see if the aphagia persisted.