In total darkness, melanophores of much of the integumentary pattern of Pseudopleuronectes americanus display intermediate melanosome distribution, whilst the alpha-adrenoceptor antagonist phentolamine evokes their complete dispersion. The intermediate condition is not attained in total darkness in locally decentralized melanophores. It is proposed that, in the absence of photic stimulation, spontaneous neural activity sustains a partial melanosome aggregation in this species.