Immune thrombocytopenic purpura (ITP) patients have characteristic anti-platelet antibodies in their circulation. To assess the interaction between such antibodies adhering on to a non-physiological surface and human platelets, normal anticoagulated blood was perfused over ITP patient plasma-coated surfaces in a parallel plate flow chamber. At 300 s-1, platelet adhesion to patient plasma-coated glass coverslips (24.0 ± 10%) was significantly higher than the adhesion to normal plasma-coated surfaces (9.8 ± 7%). When perfused at 1300 s-1, the adhesion to patient plasma-(5.1 ± 1.3%) and to normal plasma-(2.5 ± 1.2%) coated coverslips were significantly weaker. Furthermore, patient platelet binding depended on simultaneous contributions by antibodies and fibrinogen present on the plasma-coated surface, since adherence was antagonized both by normal immunoglobulins added to the perfusate, as well as by the anti-GPIIb/IIIa monoclonal antibody 16N7C2, which competes with fibrinogen for binding to its receptor on the platelet. Accordingly, platelet adhesion was only observed to coverslips coated with the plasma but not the serum of ITP patients. Hence, perfusion of normal platelets over surfaces coated with ITP patient plasma enables a functional assessment of the presence in this plasma of anti-platelet antibodies.