Previous research on cultured chick pineal cells suggests that melatonin production is modulated by Ca2+ influx through voltage-dependent Ca2+ channels. The possible existence of other ionic currents was investigated by means of whole-cell recordings from acutely isolated cells. Several different inward and outward currents were identified. Inward currents included L-type Ca2+ currents and voltage-activated tetrodotoxin (TTX)-sensitive Na+ currents. Sodium currents have not been reported previously in pineal cells of any species. These two inward currents were present in the majority of cells. Chick pineal cells also expressed several types of voltage-dependent and Ca(2+)-dependent K+ currents that differed in voltage dependence, kinetics, and pharmacology. These included two Ca(2+)-dependent outward currents which differed in sensitivity to tetraethylammonium chloride (TEA), and at least two distinct voltage-activated K+ currents. Considerable cell-to-cell variation in the amplitude and nature of the evoked outward currents was observed. These ionic currents may be important for the regulation of melatonin synthesis and the modulation of circadian rhythmicity.