Sympathetic innervation to the melanophores of a siluroid Parasilurus has been the sole instance of such innervation among lower vertebrates, in which the peripheral transmission to the effector cells is peculiarly cholinergic (Fujii and Miyashita, 1976). In an effort to find a similar case, we studied the nature of transmission of melanophores of a glass catfish Kryptopterus. Electrical nervous stimulation brought about melanosome aggregation in the melanophores. While catecholamines were found ineffective, acetylcholine and its analogues were potently active in aggregating pigment. Atropine or scopolamine interferred with the action of both nervous stimulation and acetylcholine. Physostigmine, on the other hand, augmented the cholinergic effects. The conclusion was that the transmission was cholinergic, being mediated by cholinoceptors of muscarinic type, as in the case of Parasilurus.