NEW FINDINGS: * What is the central question of this study? Nitric oxide modulates cutaneous vasodilation and sweating during an exercise-heat stress in young men. However, it remains uncertain whether these effects are reduced in black-African descendants who commonly demonstrate reduced nitric oxide bioavailability. Therefore, we assessed whether black-African descendants display reduced nitric oxide-dependent cutaneous vasodilation and sweating compared to Caucasians under these conditions. * What is the main finding and its importance? Nitric oxide-dependent cutaneous vasodilation and sweating were similar between groups, indicating reduced nitric oxide bioavailability in black-African descendants does not attenuate these heat loss responses during an exercise-heat stress. ABSTRACT: Young men of black-African descent are at an increased risk of heat related illness relative to their Caucasian counterparts. This may, in part, be due to reduced cutaneous nitric oxide (NO) bioavailability in this population, which may alter local cutaneous vasodilation and sweating. To evaluate this, we compared these heat loss responses in young men (18-30 y) of black-African (n = 10) and Caucasian (n = 10) descent during rest, exercise, and recovery in the heat. Participants were matched for physical characteristics and fitness, and they were all born and raised in the same temperate environment (i.e. Canada; second-generation and higher). Both groups rested for 10-min, and then performed 50-min of moderate-intensity exercise at 200 W/m(2) , followed by 30-min of recovery in hot, dry heat (35 degrees C, 20% RH). Local cutaneous vascular conductance (CVC%max ) and sweat rate (SR) were measured at two forearm skin sites treated with a) lactated-Ringer (Control), or b) 10 mM N(G) -nitro-L-arginine methyl ester (L-NAME, NO synthase-inhibitor). L-NAME significantly reduced CVC%max throughout rest, exercise, and recovery in both groups (both p < 0.001). However, there were no significant main effects for the NO contribution to CVC%max between groups (all p > 0.500). L-NAME significantly reduced local SR in both groups (both p < 0.050). The NO contribution to SR was similar between groups such that L-NAME reduced SR relative to control at 40 and 50 min into exercise (both p < 0.050). We demonstrate that ethnicity per se does not influence NO-dependent cutaneous vasodilation and sweating in healthy young black-African descent and Caucasian men during exercise in dry heat. This article is protected by copyright. All rights reserved.