SOME partial agonists accelerate the liberation of acetylcholine from the isolated ileum to contract it, yet also antagonize the action of the released acetylcholine1,2. We have now examined electrophysiologically the mode of action of the partial agonists3 using the guinea-pig taenia caecum which we found to have an extensive intramural inhibitory innervation but a sparse sympathetic inhibitory and cholinergic excitatory innervation.