Dynamic changes of pulpal blood flow (PBF) and gingival blood flow (GBF) induced by intra-venous injection of two kinds of vasoactive drugs were observed in dogs by means of Laser Doppler Velocimetry. Intra-venous injection of norepinephrine caused PBF to increase, corresponding to the blood pressure (BP) increase, while GBF decreased. Orciprenaline sulfate caused PBF to decrease parallel to the BP decrease, as compared with a GBF increase. The effects of these vasoactive drugs lasted longer on GBF than on PBF and BP. These results indicate that the regulation of blood flow in the dental pulp is more dependent on systemic blood pressure than on local vasoconstriction or vasodilation.