As observed for many proteins, glucose has been shown to bind non enzymatically to fibrinogen and to fibrin. The in vitro degree of glycosylation depends upon the concentration of glucose added to fibrinogen and also on the incubation period. This glycosylation induces a decrease in fibrin lysis by plasmin. On the contrary, it does not influence either fibrinogen activity as cofactor in ADP-induced platelet aggregation or the binding of thrombin onto a clot. Despite the 4 day half life of fibrinogen, since clearance of fibrinogen is exponential, it is assumed that very small quantities of fibrinogen may remain for a long time in the circulation leading to the presence of a low level of a highly glycosylated form of fibrinogen. Consequently, poorly degradable fibrin might be derived from this highly glycosylated fibrinogen and thus be responsible for capillary occlusion and also for atherosclerotic complications in the diabetic patient.