The effects of the classical morphine-like compounds and opioid peptides on the electrically-induced contractions of the myenteric plexus-longitudinal muscle strip of the rabbit ileum were studied. The results indicate that the rabbit ileum contains the new type of opiate receptor, which is not sensitive to morphine but is sensitive to enkephalins, and provides evidence that the enkephalins may function as neurotransmitters in the intestine. The action of the enkephalins was antagonized by relatively high dose of naloxone.