The sheer-stress sensor function of vascular glycocalyx heparan sulphate and hylauronic acid was investigated in vivo by assessing flow mediated dilation (FMD) before and after their removal. Heparinase III (100 mU ml-1 for 20 min) exposure (n = 6) did not significantly affect flow mediated dilation of the iliac, from 0.42 ± 0.08 mm (mean ± s.e.m.) to 0.34 ± 0.07 mm after (P = 0.12; paired Student's t test) for a statistically similar increase in shear stress; 18.24 ± 4.2 N m-2 for the control and 15.8 ± 3.6 N m-2 for the heparinase III experiment (P = 0.18). Hyaluronidase (0.14 - 1.4 mg ml-1 for 20 min) exposure (n = 8) also did not significantly reduce flow mediated dilation of the iliac, which averaged 0.39 ± 0.08 mm before and 0.38 ± 0.09 mm after (P = 0.11) for a statistically similar increase in shear stress; 11.90 ± 3.20 N m-2 for the control and 9.8 ± 3.33 N m-2 for the hyaluronidase experiment (P = 0.88). Removal of both heparan sulphate and hylauronic acid was confirmed using immunohistochemistry. Neither the heparan sulphate or the hylauronic acid components of the glycocalyx mediate shear stress-induced vasodilation in conduit arteries in vivo.