Syntaxin, synaptosome-associated protein 25 (SNAP-25) and synaptobrevin are neuronal receptors of N-ethylmaleimide-sensitive factor (NSF) and soluble NSF attachment protein (SNAP), cytosolic proteins essential for membrane transport. The expression of these SNAP receptors was investigated by immunoblotting in clonal endocrine cells; catecholamine-secreting adrenal medullary cells (PC12), growth hormone-secreting pituitary cells (GH3), and insulin-secreting pancreatic beta-cells (RINr and RINm5F). All of these receptors as well as NSF and SNAP are expressed in these cells and, co-immunoprecipitation experiments indicate that syntaxin is associated with SNAP-25 and synaptobrevin after solubilization. These results suggest that syntaxin, SNAP-25, and synaptobrevin form a complex and are involved in the secretion of hormones from endocrine cells by exocytosis.