Morphological and pharmacological findings support that different cerebrovascular nerve types have close relationships in the vessel wall and that interactions may contribute to the control of vascular tone. This study in rat investigates whether interaction in blood flow regulation occurs between sympathetic, parasympathetic and sensory nerves in the cerebral vessels. Cortical blood flow (CBF) was measured with a laser-Doppler flowmeter during electrical stimulation of one of the nerves, with or without prior denervation of one or two of the other nerves. Unilateral sympathetic stimulation significantly decreased CBF ipsilaterally. The response was unaffected in magnitude and time course by parasympathetic or sensory denervation. Sensory nerve stimulation did not significantly affect CBF, even after sympathetic denervation. Parasympathetic nerve stimulation caused a marked increase in CBF, which was similar in magnitude in the presence or absence of sympathetic innervation. However, the return to the basal CBF level after parasympathetic stimulation was prolonged after sympathetic denervation. Thus, activation of the sympathetic nerves may contribute to a rapid normalization of the enhanced CBF during parasympathetic nerve stimulation, whereas the reverse phenomenon, parasympathetic normalization of the sympathetically induced CBF reduction, does not occur.