Erythrophores in isolated scales of the motleystripe rainbowfish, Halichoeres tenuispinnis, assumed an unstable state in physiological saline solution, changing irregularly their state into a half-aggregated state. The present paper described a method for studying physiological responses of chromatophores that failed to keep a stable state of pigment granules in a physiological saline solution and, using this method, adrenergic regulation of movements of erythrophores in Halichoeres tenuispinnis was investigated. The erythrophores maintained the dispersed state in the saline solution for at least 30 min by pretreatment with isoproterenol (10-7M). The treatment seemed not to affect their responses. Norepinephrine-induced aggregation was shown to be mediated by alpha2 adrenoceptors on pharmacological ground. It was also shown that the erythrophores possessed beta adrenoceptors mediating the dispersion of the pigment granules and that the stimulation of the beta adrenoceptors was associated with an increase of the cAMP content within the cells.