When histological sections of noninnervated kidney grafts of pituitary pars intermedia were immunohistochemically processed for the demonstration of either alpha melanocyte-stimulating hormone or adrenocorticotropic hormone, chromophilic (dark) and chromophobic (light) cells could be detected. The latter, which were not detected in the intact intermedia, were interpreted as hyperactive cells, since they lacked secretory granules and displayed an increased nuclear area. The administration of ergocryptine prevented the development of light cells. Moreover, after chronic stress (swimming), some cells appeared less intensely granulated than dark cells. The results suggest that the pars intermedia is composed of parenchymal cells with different sensitivities to dopamine. Light cells would be subject to a greater dopamine-induced inhibitory influence than dark cells. The appearance of partially degranulated cells after stress points to a participation of the grafts in this event and indicates that innervation of the intermedia is not an indispensable condition for its contribution to stress.