Antibodies were characterized as inhibiting VWF binding interactions to FVIII, collagen, and platelet receptor GPIbα. Plasma from the 9 patients with type 3 VWD who are antibody positive, along with the T3 Ab^– control for comparison, was mixed and preincubated with rVWF to allow for antibody/VWF complex formation, then measured for VWF binding function using VWF:F8B, VWF:CB3, VWF:CB4, and VWF:GPIbM ELISA methods. (A) CB3, CB4, GPIbM, and F8B indicate inhibited function of VWF binding to collagen type III, collagen type IV, platelet receptor GPIbα, and FVIII, respectively. Percent of the patients with each type of inhibitor revealed 33% of the samples contained nonneutralizing (NN) antibodies, whereas the majority of antibody samples inhibited VWF:F8B (56%) followed by VWF:CB3 (33%). (B) Percent of VWF binding inhibition when compared with the T3 Ab^–/rVWF control ranged in severity between undetected (shaded, ≤10%) and ≥94% (VWF:CB3). Among the 8 IgG (●) and 1 IgM (■) anti-VWF samples, FVIII and collagen III to VWF inhibition were found to be most prevalent and had higher degrees of inhibitory function.