In view of the possible role of the hippocampus in the neuroendocrine regulation of ACTH secretion, experiments were conducted in rats and cats in which cortisol (C) and corticosterone (CS) were applied by iontophoresis and pressure microinjection while recording from single identified pyramidal cells in the dorsal hippocampus, using multi-barrelled microelectrodes. None of the more than 500 cells tested responded with a significant change in firing rate. The possible relation of these findings to neuroendocrine regulation of ACTH secretion is discussed.