A recent study reported that the vasoactive intestinal peptide (VIP) fragment VIP_10-28 inhibited the rise in skin blood flow during whole body heating. Although VIP_10-28 only partially blocked exogenous VIP-mediated vasodilation and tended to increase baseline skin blood flow, this finding was taken to suggest a role for VIP in active vasodilation. Consistent with this concept, our laboratory has reported that the NO pathway and H1-receptor activation is common to both exogenous VIP-mediated dilation and active vasodilation. Our goal in the present study was to further examine the specific role for VIP in cutaneous active vasodilation by using VIP_10-28 to antagonize VIP-mediated dilation in the presence of NO-synthase inhibition and H1-receptor antagonism. Combined, a total of thirty subjects volunteered for four studies. Study 1 (n = 12) examined whether VIP_10-28 antagonizes vasodilation to exogenous VIP in the skin via inhibition of NO-dependent mechanisms. Study 2 (n = 6) investigated the skin blood flow response during hyperthermia in skin sites receiving VIP_10-28 alone and in combination with NO synthase inhibition. Study 3 (n = 6) examined vasodilation during hyperthermia in skin sites receiving VIP_10-28 alone and combined VIP_10-28 and H1 receptor antagonist. Due to differences in our findings and those previously published, Study 4 (n = 6) was designed to investigate whether an increase in baseline skin blood flow would result in a diminished rise in skin blood flow, similar to the previously reported observation with VIP_10-28 during hyperthermia. Red blood cell flux was measured over each site using laser-Doppler flowmetry and cutaneous vascular conductance (CVC; laser-Doppler flux/mean arterial pressure) was normalized to maximal vasodilation (28 mM sodium nitroprusside). In contrast to previous studies, the presence of VIP_10-28 augmented vasodilation to exogenous VIP (P <0.05 vs. control; study 1) and whole body heating (P <0.05 vs. control; study 2). The addition of NO synthase inhibitor had no affect on the augmented dilation to exogenous VIP or during hyperthermia (P >0.05). In study 3, H1 receptor antagonist also had no affect on the augmented skin blood flow during hyperthermia in the presence of VIP_10-28 (P >0.05 vs. VIP_10-28). In study 4, the rise in skin blood flow ( %CVC_max) was attenuated when baseline skin blood flow was elevated prior to whole body heating. Our results suggest VIP_10-28 is an unsuitable antagonist for examining a role for VIPmediated dilation in human skin.