Nitroglycerin (NTG) selectively vasodilates muscular conduit arteries. Whether other nitric oxide (NO) donors and natriuretic peptides have similar effects is unknown. The aim of this study was to compare effects of NTG, sodium nitroprusside (NP) and brain natriuretic peptide (BNP) on the radial artery (a muscular conduit artery) and forearm resistance vasculature. Phentolamine (PHT), a vasodilator with minimal vasodilator effects on conduit arteries was used as a control. Healthy normotensive men aged 19–45 years were studied. The right brachial artery was cannulated using a 27 gauge needle and an intra-arterial infusion of each vasodilator (PHT, 10, 30 and 100μg/min, n = 9; NTG 0.03, 0.1, 0.3, 1.0, 3.0 μg/min, n = 8. NP, 0.3, 1, 3 μg/min,n = 11; BNP 0.03, 0.1, 0.3, 1, 3 μg/min n = 8) given on separate occasions or after washout. Forearm blood flow (FBF) was measured by venous occlusion plethysmography and change in radial artery diameter by ultrasound. The percentage change in diameter for different drugs was compared at doses producing the same change in FBF (DFBF). The efficacy of dilation of the radial artery was NTG>NP >BNP>PHT. Radial artery dilation by NTG and NP but not BNP was greater than that by PHT (P <0.05) and radial dilation by NTG greater than that by BNP (P<0.05). These results demonstrate that drugs acting on the guanylyl cyclase – cGMP pathway have differential actions on muscular conduit arteries.