The opioid receptor, delta 1, also known as delta opioid receptor or simply delta receptor, abbreviated DOR, is an opioid receptor that has enkephalins as its endogenous ligands.Pharmacological studies and molecular cloning have led to the identification of three different types of opioid receptor, mu-type, delta-type and kappa-type, also designated MOR-1, DOR-1 and KOR-1, respectively. MOR-1 is a receptor for beta-endorphin, DOR-1 is a receptor for enkephalins, and KOR-1 is a receptor for dynorphins.