It is known that in normal mice and rats, about 10,000 neurons are present on each side of the suprachiasmatic nucleus (SCN). It was reported, however, that the circadian locomotive activity rhythm was completely lost in anophthalmic mice with less than 3000 neurons bilaterally in their SCNs. Unilateral blindness is sometimes found among these hereditary microphthalmic rats. In these cases the circadian locomotive activity rhythm was synchronized with a light-dark cycle. It was determined whether the microphthalmic rats showed the hyperglycemic response to intracranial injections of 2-deoxy-D-glucose (2DG) given either in the subjective light or dark period. The morphological changes in the SCNs of surgical and congenital blind rats seem to reflect the absence of hyperglycemic responses to 2DG and electrical stimulations of the SCN and LPBD. Therfore, it seems quite reasonable to conclude that neurons in the SCN which receive retinal inputs are involved in central regulation of energy metabolism.