Glucagon-like peptide-1 (GLP-1), an incretin, is used to treat diabetes mellitus, inhibited vagal activity, and activated nitrergic pathways in humans. In rats, GLP-1 also increased sympathetic activity, heart rate, and blood pressure (BP). However, the effects of GLP-1 on sympathetic activity in humans are unknown. Our aims were to assess the effects of a GLP-1 agonist with or without ₂ adrenergic or nitrergic blockade on autonomic nervous functions in humans. In this double-blind study, 48 healthy volunteers were randomized to GLP-1-(7-36) amide, a low dose of the nitric oxide synthase (NOS) inhibitor NG-Monomethyl-L-Arginine acetate (L-NMMA), the ₂-adrenergic antagonist yohimbine, or placebo (i.e., saline) alone or in combination. Sixteen subjects were subsequently randomized to GLP-1 or GLP-1 plus a higher dose of L-NMMA. Hemodynamic parameters, plasma catecholamines, and cardiac sympathetic as also parasympathetic modulation were measured by spectral analysis of heart rate. Thereafter, the effects of GLP-1-(7-36) amide on muscle sympathetic nerve activity (MSNA) were assessed by microneurography in 7 subjects. GLP-1 increased (p = 0.02) MSNA but did not affect cardiac sympathetic or parasympathetic indices as assessed by spectral analysis. Yohimbine increased plasma catecholamines and the low frequency (LF) component of heart rate power spectrum, suggesting increased cardiac sympathetic activity. Both doses of L-NMMA increased the BP and reduced the heart rate but did not affect the balance between sympathetic and parasympathetic activity. GLP-1 increases skeletal muscle sympathetic nerve activity but does not appear to affect cardiac sympathetic or parasympathetic activity in humans.