Histamine content and histidine decarboxylase activity in cortex and hypothalamus, together with histamine content in peripheral nervous structures were examined in normal and electrically stressed guinea-pigs. A significant increase in histidine decarboxylase activity in hypothalamus and cortex together with concomitant decrease in histamine content in hypothalamus have been found. Electric shock causes also a decrease in histamine content in spinal cord, spinal ganglia, dorsal roots and sensory nerve. The function of histamine in nervous system is discussed.