Cholinergic, adrenergic and some other drugs known as neurotramsmitters were tested on the whole (intact) isolated tube feet of A. amurensis and on those dissected to expose the connective tissue layer (cleaned tube feet). Acetylcholine (ACh) and GABA caused contractions of the tube feet, being 1000 times as potent on the cleaned tube feet as on intact ones. Catecholamines, were more effective on the intact tube feet. ACh potency (EC50 = 1 .times. 10-6 M) was greatly increased in the presence of neostigmine or physostigmine. Nicotinomimetics were generally 10- to 100-fold as potent as muscarinomimetics. More or less selective suppression of responses to nicotinomimetic or to muscarinomimetic agents by appropriate blocking agents suggests the existence of 2 kinds of cholinoreceptors in the tube foot muscles. The inability of cholinergic blocking agents to prevent GABA responses, and the fact that the muscle desensitized to GABA still reponds to ACh, sugg that ACh and GABA interact with different receptors. Glycine and 5-HT [5-hydroxtryptamine creatinine sulfate] were ineffective; L-glutamic acid produced only small contractions and histamine caused relaxations.