The last decade has been the most prolific and stimulating period in the area of prostaglandin (PG) study. Since PGs were found in the hypothalamus and cerebrospinal fluid, and were released from the central nervous system (CNS) spontaneously and in response to chemical or electric stimulation, many investigators have been engaged in studying their effects in the CNS. In fact, PGs have a wide range of pharmacological actions in the CNS. Relatively large doses of PGs have to be given centrally to produce some effects. On the other hand, some types of PGs, when applied centrally in doses of a few ng, stimulate the hypothalamus or the pituitary gland to increase secretion of hypothalamic and anterior and also posterior pituitary hormones. Physiological investigations of PGs have been aided by the use of inhibitors of their synthesis; aspirin, indomethacin etc. These compounds inhibit secretion of the hormones from the hypothalamus as well as the pituitary, suggesting that endogenous PGs exert a functional role for the hormone secretion. To produce fever, PGEs have to act on the preoptic anterior hypothalamus, and aspirin and indomethacin decrease fever produced by pyrogens but not PGEs. Pyrogens produce fever by increasing synthesis and release of PGEs. Hypothalamic PGEs play a role as a central transmitter or modulator in temperature regulation.