This study investigates the effects of hyperinsulinemia on sympathetic neural activity and vascular resistance in normotensive humans. Fourteen healthy males were infused with low (38 mU/m/min) and high (76 mU/m/min) doses of insulin while maintaining constant blood glucose levels. Muscle sympathetic nerve activity (MSNA), forearm blood flow, heart rate, and blood pressure were measured. Plasma insulin levels increased significantly during both insulin infusions, and MSNA also increased significantly. Plasma norepinephrine levels rose during both insulin infusions and recovery, but plasma epinephrine levels remained unchanged. Despite the increased MSNA and norepinephrine levels, forearm blood flow increased and vascular resistance decreased during both insulin infusions. Systolic blood pressure did not change significantly, but diastolic pressure decreased by ~4–5 mmHg. The study suggests that acute increases in plasma insulin within the physiological range elevate sympathetic neural outflow but produce forearm vasodilation and do not significantly increase arterial pressure in normal humans.This study investigates the effects of hyperinsulinemia on sympathetic neural activity and vascular resistance in normotensive humans. Fourteen healthy males were infused with low (38 mU/m/min) and high (76 mU/m/min) doses of insulin while maintaining constant blood glucose levels. Muscle sympathetic nerve activity (MSNA), forearm blood flow, heart rate, and blood pressure were measured. Plasma insulin levels increased significantly during both insulin infusions, and MSNA also increased significantly. Plasma norepinephrine levels rose during both insulin infusions and recovery, but plasma epinephrine levels remained unchanged. Despite the increased MSNA and norepinephrine levels, forearm blood flow increased and vascular resistance decreased during both insulin infusions. Systolic blood pressure did not change significantly, but diastolic pressure decreased by ~4–5 mmHg. The study suggests that acute increases in plasma insulin within the physiological range elevate sympathetic neural outflow but produce forearm vasodilation and do not significantly increase arterial pressure in normal humans.