Electrical activity in the form of action potentials (spikes) was discovered in normal anterior pituitary cells obtained from rats by tissue dissociation and maintained in culture. Passage of outward current through the microsuction electrodes used for recording often increased spike frequency in spontaneously active cells or initiated spikes in cells previously electrically silent. Spiking persisted in the presence of tetrodotoxin and in the absence of sodium, but was inhibited by the calcium blockers D600 and lanthanum. Such spikes appear, therefore, to be calcium spikes, but contributions to spiking by other ions are not excluded. The stimulant hypophysiotropic peptide thyrotropin-releasing hormone elicited spiking in about ten percent of the cells on which it was tested. These cells are possibly thyrotrophs and mammotrophs, the physiological target cells for this hormone. These results, considered along with existing evidence that adenohypophyseal secretion requires calcium and is elicited by calcium ionophores, prompt the conclusion that action potentials involving calcium influx participate in stimulus-secretion coupling in the anterior pituitary. It may be by stimulating or modulating such electrical activity (with hypophysiotropic hormones) that the brain regulates anterior pituitary secretion.