The aim of the present study was to explore the electrophysiological properties of pituitary cells from Atlantic cod (Gadus morhua), as a basis for future studies of the signaling pathways involved in the control of pituitary secretion in this species. Primary cultures of pituitary cells from maturing Atlantic cod were prepared by trypsin treatment and mechanical dispersion. Electrophysiological recordings were performed using the perforated patch clamp method. A subpopulation of large cells were selected for recordings. Spontaneous action potentials were observed in about 30% of the cells. The action potentials displayed a fast initial spike followed by a prolonged plateau. Correspondingly, the inward current elicited by depolarizing steps consisted of both a transient, tetrodotoxin-sensitive Na<sup>+</sup> component and a nifedipine-sensitive Ca<sup>2+</sup> component that was sustained when Ba<sup>2+</sup> replaced Ca<sup>2+</sup> as current carrier. The outward current was partially blocked both by 5 m M tetraethylammonium and 10 m M 4-aminopyridine. The voltage-activated ion channels present in these cells largely correspond to the ion channels of pituitary cells in other teleosts (goldfish, Carassius auratus, and tilapia, Oreochromis mossambicus) and mammals, although differences exist regarding the shape and duration of action potentials.