Background: Experimental animal data suggest that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) might reduce enhanced sympathetic activity, a hallmark of hypertensive patients. This hypothesis was tested for the first time in patients with primary hypertension. Methods and Results: Using a prospective, randomized, placebo-controlled, double-blind, cross-over design, a proof-of-principle trial was performed in 13 patients with mild to moderate primary hypertension, who were randomly assigned to a regimen of atorvastatin (80mg/day) for 3 weeks, followed by placebo for 3 weeks or to a regimen of placebo for 3 weeks, followed by atorvastatin (80mg/day) for 3 weeks. Microneurography was used at the end of each treatment period to measure sympathetic nervous system activity (muscle sympathetic nerve activity: MSNA). Heart rate variability (HRV) and plasma norepinephrine concentrations were also measured. Additionally, effects on blood pressure (BP) and heart rate (HR) were assessed by 24-h ambulatory BP measurement. Atorvastatin reduced postganglionic MSNA (atorvastatin 35.0±2.0 vs placebo: 39.2±1.5 bursts/min, P=0.008) and heart frequency corrected MSNA (atorvastatin: 58.5±2.0 vs placebo: 64.7±3.0 bursts/100 beats, P=0.02). Atorvastatin had no significant effect on plasma norepinephrine levels, HRV, BP or HR. Conclusions: In patients with mild to moderate hypertension, atorvastatin reduces postganglionic MSNA, which supports the hypothesis that HMG-CoA reductase plays a role in sympathetic nervous system activity. (Circ J 2010; 74: 2622-2626)