Enkephalin-like material in adrenal gland consists of high and low molecular weight forms. The high molecular weight (HMW) forms (MW greater than 1000) are N-terminal extended met5-enkephalins and show no opiate-like activity unless trypsinized. They are preferentially located in chromaffin cells and seem to exist also in blood suggesting that they may be released into blood chromaffin cells. In the plasma, the HMW forms were found to be very stable. The low molecular weight (LMW) fraction also consists of multiple forms including met-5- and leu-5- enkephalins and three other enkephalin-like peptides. They bind to opiate receptors with high affinity suggesting that they may function as opiate ligands in adrenal glands; they can be detected in splanchnic nerves and also in adrenal medulla. In view of the existence of opiate receptors on chromaffin cells and the presence of opiate peptides in the splanchnic, LMW enkephalin-like peptides may exert their action on chromaffin cells.