Studies have demonstrated that serum protein adsorption onto silk fibroin-based biomaterials dramatically changes when the conformation of this natural polymer is rearranged by engineering procedures. In the present study, attention was paid to the binding of fibrin(ogen) to fibroin fibers and regenerated films. The fibroin specimens were incubated either in human plasma or in a fibrinogen solution to which thrombinwas added to activate the polymerization of the precursor into the final product, fibrin. The experiments were carried out in the presence and absence of calcium to investigate the role of calcium-dependent enzymes in the binding process. The two types of samples were analyzed by SEM, the micrographs showed completely different interactions with fibrinogen. Films did not show any visible fibrin polymerization, whereas the fibers were bound to the fibrin bundles by calcium-independent mechanisms.