The myenteric plexus-longitudinal muscle preparation of the guinea pig ileum has been well characterized with respect to modulators of the release of acetylcholine (ACh). We have recently succeeded in preparing synaptosomes from this preparation and plan to study the mechanism of action of a variety of agents on the uptake of choline and release of ACh. To study release, the preparation will be preincubated with (3H) choline in order to make radioactive ACh. Release of the transmitter is effected by depolarization on the addition of either KC1 or veratridine. Agents to be tested for their effect on release include atropine, morphine, oxotremorine, norepinephrine, serotonin, carbachol, and somatostatin. Other projects to be undertaken with this preparation involve the antimony analog of choline, and the possibility that Na-K ATPase is involved in the release of the transmitter.