DesAA-fibrin Sepharose was produced by treating fibrinogen-Sepharose with batroxobin. DesAA-fibrin Sepharose was mixed with different concentrations of fibrinogen and at different ratios, and incubated with preactivated FXIII. After 2 hours at 37 degrees C, the Sepharose beads were separated by centrifugation and non-crosslinked fibrinogen was removed by twice times washing with guanidinium chloride, pH 4.1. Under these experimental conditions specific crosslinking of fibrinogen to immobilized desAA-fibrin by FXIIIa was found. These results support the concept of a specific interaction between fibrinogen and fibrin involving polymerization which enables FXIIIa to crosslink fibrin to fibrinogen being in an half-staggered overlap position but not in DD-long contact.