Since intravascular and endoparietal fibrin deposition is thought to be involved in the development of atherosclerosis, we measured factor XIII activity and its subunit ‘a’ and ‘b’ concentrations against a background of other haemostasis parameters in diabetics with angiopathy and in 2 control groups (healthy subjects and diabetics without vascular complications). Diabetics with angiopathy revealed a significant increase of factor XIII activity as well as its subunit concentrations. They also had significantly elevated antithrombin III, α2 macroglobulin, α1 antitrypsin, C\ inhibitor, fibrinogen, FDP concentrations and prolongation of euglobulin lysis time. The highest factor XIII levels were found in diabetics with renal failure. We suppose that increased factor XIII level and other observed changes of haemostasis in patients with diabetic angiopathy might promote intravascular and endoparietal fibrin deposition and contribute to the development of atherosclerotic complications of diabetes.