To investigate whether the responses of neurones in the lateral hypothalamus and substantia innominata associated with the sight of food could control the responses of the hungry monkey to the food, the latency of activation of these neurones by food was measured. It was found that when an electromagnetically operated wide-aperture shutter opened to reveal food or non-food objects, these hypothalamic neurones responded with a latency of 150--200 msec to the food objects, and did not respond to the non-food objects. To measure the latency of the monkey's responses to the food, a visual discrimination task was set in which the monkey could lick a tube to obtain fruit juice if a food-realted visual stimulus was shown, but obtained hypertonic saline, which was aversive, if a different visual stimulus was shown. In this situation the typical latencies of the neuronal responses to the food were 150--200 msec, of the lick responses 350--500 msec, and of the EMG activity associated with these lick responses 250--400 msec. Thus the responses of these hypothalamic neurones precede the monkey's responses to the food, and could mediate the feeding and other responses of the animal to the food. It was also shown that a different population of hypothalamic neurones with responses associated with the sight of aversive visual stimuli had response latencies of 150--200 msec.