The purpose of the present study was to investigate the nervous control of gingival blood flow in cats. Gingival blood flow was measured by laser Doppler flowmeter in 75 cats during electrical stimulation and cutting or ligation of the inferior alveolar nerve and cervical sympathetic nerve without sympathectomy or pretreatment with adrenoceptor blocking agents. Three different patterns of responses in gingival blood flow were observed following electrical stimulation of the inferior alveolar nerve in cats. In 45 cats there was an increase in blood flow, in 4 cats a decrease in blood flow, and in 7 cats a biphasic change consisting of an initial decrease and a successive increase in blood flow. The vasodilator effect was significantly reduced by pretreatment with (d-Pro2, d-Trp7,9)-substance P, tripelennamine, and methysergide. Pretreatment with cimetidine, atropine, hexamethonium, phentolamine, or propranolol had no effect on vasodilatation. The vasoconstrictor response was completely inhibited by pretreatment with phentolamine; in this case the vasodilator response appeared after stimulation of the inferior alveolar nerve. Ligation or cutting of the inferior alveolar nerve always elicited an increase in gingival blood flow. Cutting the cervical sympathetic nerve had no effect on gingival blood flow in 8 of 10 cats and caused an increase in gingival blood flow in 2 cats; however, electrical stimulation of the cervical sympathetic nerve always caused a decrease in gingival blood flow in the cats investigated. The present results suggest that cat gingival blood flow is controlled by sympathetic α-adrenergic fibers for vasoconstriction and by sensory fibers and mast cells for vasodilatation.