The effects of pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide isolated from mammalian hypothalamus, was investigated on neurotransmitter release from clonal rat pheochromocytoma PC12 cells and cultured rat cerebellar granule cells. We found that PACAP38 stimulates the neurotransmitter release from PC12 cells by two distinct mechanisms in different concentration ranges. In the lower concentration range (<1 nM), PACAP38 enhanced depolarization-and ionomycin-dependent dopamine release without mobilizing intracellular Ca2+, while in the higher concentration range (>1 nM), PACAP38 induced profound Ca2+ influx and concomitant dopamine release from PC12 cells. In cultured rat cerebellar granule cells, PACAP38 failed to increase intracellular Ca2+; however, it enhanced depolarization-dependent glutamate release remarkably. These results indicate that PACAP38 enhances Ca2+-dependent neurotransmitter release by modulating step(s) subsequent to Ca2+ entry.