This document discusses the evaluation of recombinant clotting factor VIII concentrates. It analyzes the heterogeneity and purity of different recombinant factor VIII preparations before and after thrombin digestion using techniques like SDS-PAGE, 2DE electrophoresis, and gel digestion. The results show bands corresponding to truncated recombinant factor VIII as well as the presence of contaminating proteins like haptoglobin and albumin. Thrombin cleavage was found to remove bands in the SDS-PAGE of the inactive factor VIII pro-cofactor. The conclusions state that 2DE is better than SDS-PAGE for assessing purity and that the use of recombinant factor VIII does not rule out contaminants.