Recent studies indicate that CRTTP patients have excessive shear stress-induced platelet aggregation that is associated with the presence of ULvWF multimers in their plasma and increased vWF-binding to their platelets by flow cytometry. In these CRTTP patients, relapses, excessive shear-aggregation and the presence in their plasma of ULvWF forms are all reversed by the infusion of normal FFP or substances devoid of the largest vWF multimers found in plasma (cryoprecipitate-poor plasma or cryosupernatant; solvent/detergent-treated plasma) without the need for concurrent plasmapheresis. This constellation of observations, along with reports of increased vWF in TTP platelet thrombi, increases the probability that ULvWF multimers derived from injured or abnormal endothelial cells induce aggregation during TTP episodes in high-shear regions of the microcirculation.