Platelet‐Aggregating Activity in Neuraminidase‐Treated Human Cryoprecipitates: Its Correlation with Factor‐VIII‐Related Antigen

S ummary . Neuraminidase induced platelet‐aggregating activity in cryoprecipitates from three normal subjects and from six haemophilia A patients; the effect was not or only slightly seen in cryoprecipitate from two patients with von Willebrand's disease; development of this activity was linked to the presence of factor‐VIII‐related antigen. These findings may be of interest for the diagnosis of von Willebrand's disease and suggest a reaction sequence of major importance for human haemostasis.