The muscle receptor organs of Homarus americanus were examined histochemically for cholinesterase, using the thiocholine method of Koelle. Cholinesterase occurs in the sensory neurons and in motor and accessory fibers, but its highest concentration is reached in the interelated regions of the muscle receptor organs. The somatic cytoplasm of the fast-adapting neuron contains more cholinesterase than that of the slow-adapting cell. Neuromuscular endings of some of the accessory and motor fibers are tentatively identified.