Gonadotropin affiliated by biological and immunochemical properties to the luteinizing hormone of the hypophysis was revealed in the purified extracts from the bovine pineal glands. Biological properties of gonadotropin from the pineal glands were assessed by the reactions specific of the luteinizing hormone. Immunochemical properties of gonadotropin were studied by means of gel-precipitation in agar gel, immunoelectrophoresis and radioimmunochemical analysis. It was found that the specific content of gonadotropin in the epiphysis was 80 times lower than the specific content of the luteinizing hormone in the hypophysis, but exceeded the LH concentration in the blood serum 555 times and in the cerebrospinal fluid 6.8 times. Immunoreactive LH was absent in the extracts of the brain cortex, the liver and the ovaries. A theoretical interpretation of a possible physiological role of the LH-like gonadotropin in the endocrine regulation of the reproductive function of the organism is given in this work.