The PFA-100 measures platelet plug formation under shear stress and is strongly dependent on von Willebrand Factor (VWF) levels in plasma. We therefore hypothesized that elevated VWF levels, possibly as a result of acute inflammation, adversely influence PFA-100 results. Healthy volunteers received either 2 ng/kg endotoxin or placebo in a randomized controlled trial. Four hours after endotoxin (but not placebo) infusion VWF levels increased by 85%, collagen epinephrine-induced closure time (CT) decreased by 47% and collagen ADP-CT decreased by 38% (P < 0.0001) respectively. In conclusion, systemic inflammation has a major impact on the results obtained by PFA-100 and may confound interpretation of platelet function.