Peptide synthesis and release in primary dissociated nerve cell cultures have been studied using a very high specific activity, radiolabeled amino acid precursor, high-performance liquid chromatography and amino acid sequencing of purified peptides. The combined use of these methods has resulted in the rigorous demonstration of ribosomal synthesis of methionine-enkephalin by spinal cord cells, the basal release of methionine-enkephalin by spinal cord and substance P by brain cells, the tetrodotoxin sensitivity of this spontaneous release, and the potassium depolarization induced release of both peptides in a calcium dependent manner. This approach to the study of the development and biological chemistry of peptidergic neurons is recommended as a model because of the accessibility of the cells under conditions of ongoing physiologic function and the unequivocal nature of the chemical characterization of synthesized peptides.