We examined whether a sympathetic cholinergic mechanism contributed to increased blood flow of the exercising muscle at the onset of voluntary static exercise in conscious cats. After six cats were operantly conditioned to perform static bar-press exercise with a forelimb while maintaining a sitting posture, a Transonic or pulsed Doppler flow probe was implanted on the brachial artery of the exercising forelimb and catheters were inserted into the left carotid artery and jugular vein. After the baseline brachial blood flow and vascular conductance decreased and became stable in progress of postoperative recovery, the static exercise experiments were started. Brachial blood flow and vascular conductance began to increase simultaneously with the onset of exercise. Their initial increases reached 52 ± 8% and 40 ± 6% at 3 s from the exercise onset, respectively. Both a sympathetic ganglionic blocker (hexamethonium bromide) and atropine sulfate or methyl nitrate blunted the increase in brachial vascular conductance at the onset of static exercise, whereas an inhibitor of nitric oxide synthesis (N-nitro-L-arginine methylester) did not alter the increase in brachial vascular resistance. Brachial blood flow and vascular conductance increased during natural grooming behavior with the forelimb in which the flow probe was implanted, whereas they decreased during grooming with the opposite forelimb and during eating behavior. Thus it is likely that the sympathetic cholinergic mechanism is capable of evoking muscle vasodilatation at the onset of voluntary static exercise in conscious cats.