In acute experiments on anaesthetized kittens, studies have been made on the background and the evoked activity of hypothalamic neurons elicited by sensory stimuli. It was shown that already from the 2nd day of postnatal life, it is possible to observe the background impulse activity of the neurons in the posterior hypothalamus. The evoked reactions to stimulation of the sciatic nerve were recorded at the 4-5th day of postnatal life. At early stages of ontogenesis, both phasic and tonic types of neuronal reactions are presented in the hypothalamus, the former being more frequent. To the end of the 3rd week, neuronal reactions in the hypothalamus do not reach definitive pattern.