A modification of the method of Hess and Udenfriend (1959) for the extraction and identification of tryptamine, as well as a gas chromatographic method for identifying tryptamine, has been described. Tryptamine, using these methods, as well as thin layer chromatography, has been identified in steer, dog and human brain. Tryptamine was not found in the rat brain. In the dog, isocarboxazid increased brain and spinal cord tryptamine levels two or three times. In view of the fact that tryptamine resembles LSD-like hallucinogens in many of its actions, it is suggested that tryptamine may be a naturally occurring hallucinogen that may play a role both in normal and pathologic functioning of the brain.