[Met5]-Enkephalin, amide is an agonist for δ opioid receptors as well as putative ζ (zeta) opioid receptors. [Met5]-Enkephalin at 0.1 nM, 10 nM, and 1 μM significantly reduces the total number of glial cells in culture. [Met5]-Enkephalin, amide acts via δ-opioid receptor to inhibit pelvic nerve-evoked contractions of cat distal colon. [Met5]-enkephalin causes concentration-dependent, reversible inhibition of pelvic nerve-evoked contractions, with an IC50 value of 2.2 nM. [Met5]enkephalin at a concentration (3 nM) which produces a large inhibition of neurogenic contractions, has no effect on contractions to exogenous acetylcholine.