In addition to its important functions in angiogenesis, wound healing, bone biology, immunology, pregnancy, and adipogenesis, transglutaminase factor XIII is an outstanding determinant of clot characteristics. Factor XIII mediates clot stability by covalent cross-linking of fibrin-fibrils and inhibition of fibrinolysis. For decades it was assumed that factor XIII mediates the formation of a 3-dimensional net structure of the clot. It was the aim of our experiment to prove this thesis.