Data on fibrinolysis in diabetes mellitus are still unclear, as is the role of hyperglycaemia on this topic and the possibility of any therapeutic intervention. In this study we examined fibrinopeptide A, tissue plasminogen activator and plasminogen activator inhibitor plasma levels in Type 1 diabetic patients compared to matched healthy normal controls, and the effect of induced hyperglycaemia on these parameters. At the same time the effect of a glycosaminoglycan, Sulodexide, administration during hyperglycaemia was evaluated. Fibrinopeptide A and plasminogen activator inhibitor were increased while tissue plasminogen activator was decreased in Type 1 diabetic patients, in the basal state. Induced hyperglycaemia increases fibrinopeptide A formation and tissue plasminogen activator concentrations, while it decreases plasminogen activator inhibitor levels more in normal subjects than in diabetic patients. Sulodexide consistently reduces this phenomenon. This study shows an altered fibrinolytic response to increased thrombin activation in Type 1 diabetic patients and suggests that the administration of the glycosaminoglycan, Sulodexide, may help to reduce this phenomenon.