AbstractThe plasma free N‐terminal fibronectin 30‐kDa domain was measured in 44 type 1 diabetic patients and in 20 healthy subjects. A significantly raised mean concentration of a free N‐terminal fibronectin 30‐kDa domain was found in plasma of diabetic patients with proliferative retinopathy as compared with healthy persons (P<0·001). A positive correlation was observed between free N‐terminal fibronectin 30‐kDa domain and von Willebrand factor in plasma of all examined subjects (r= 0·62,P<0·01). A similar correlation was present between 30‐kDa domain and albuminuria (r= 0·56,P<0·01). However, no relationship was found between fibronectin 30‐kDa domain and control of diabetes as assessed by fructosamine concentration. The free N‐terminal fibronectin 30‐kDa domain may be used as a marker of actual endothelial cell