['Endothelial dysfunction has been found to be present in subjects with both small and medium-size blood vessel vasculitides. We assess whether endothelial dysfunction was also present in patients with biopsy-proven giant cell arteritis (GCA) and whether it might be improved following steroid treatment.', 'Endothelial function was determined in cross-sectional and longitudinal studies of 6 patients with biopsy-proven GCA diagnosed between January and May 2002 by measuring flow-mediated endothelial-dependent and independent vasodilatation (EDV and EIV) by brachial ultrasonography. Patients were assessed for endothelial function within 48 hours after the onset of steroid therapy, 4 weeks after the onset of steroid therapy, and 2 years after the disease diagnosis.', 'EDV was significantly impaired in patients with GCA compared with 12 matched controls [mean 2.9%, median 2.45% (range 2.1% to 4.7%) vs mean 6.5%, median 6.6% (range 3.9% to 9.3%) in matched controls; p = 0.002]. However, no significant difference existed between patients and controls in EIV. Significant improvement of EDV after the suppression of inflammation was achieved. At Week 4 after the onset of steroid therapy all 6 patients showed enhanced responses (p = 0.028). This improvement of EDV was still present when steroid treatment was ended, 2 years after diagnosis.'] Does steroid therapy improve endothelial function in patients with biopsy-proven giant cell arteritis?