The aim of the present study was to examine the effects of stimulation delivered to the teeth neighboring the canine on the pulpal blood flow (PBF) and intradental nerve activities (INA) of the canine. Twenty cats were anesthetized with pentobarbital sodium (i.v., 30mg/kg), and mustard oil (MO) was applied to a pulp-exposed cavity prepared at the tooth crown for 10 minutes in one of the following teeth; upper second premolar, third premolar or third incisor. The PBF and INA were recorded simultaneously from the canine. MO to the second premolar or third incisor significantly increased the PBF of the canine to 162.0+/-65.8% (n=16) and 158.8+/-48.9% (n=6), respectively (P<0.05). On the other hand, MO to the third premolar did not significantly increase the canine PBF [122.3+/-20.1% (n=9), P>0.05]. In addition, INA were elicited from the canine after MO application to the second or third premolar in 4 cats. These results indicate that the canine PBF is increased by MO application to the neighboring teeth. This phenomenon might be based upon the axon reflex of branched nerve fibers innervating plural teeth.