The separately cultured smooth muscle and endothelial cells derived from dissociated cerebral microvessels are characterized by high content of glycogen. Norepinephrine induces glycogenolysis while 5-hydroxytryptamine stimulates glycogenesis in both cell types. The endogenous glucose of the endothelium but not that of the smooth muscle serves as a direct source for the 5-HT enhancement of glycogen formation. Indomethacin, the known inhibitor of cyclooxygenase modulates the glycogen content in the smooth muscle only. These findings strongly suggest that the carbohydrate metabolism of each cell has a distinct control mechanism compatible with the underlying integral microvascular function.