To evaluate the influence of fibrin cuffs on the transcutaneous oxygen tension in patients with chronic venous insufficiency (CVI) we performed a prospective comparative study in an out-patient dermatological department of a district hospital in the Netherlands. 16 patients with CVI grade II or III, 6 patients with porphyria cutanea tarda (PCT) without any sign of CVI, 4 patients with clinical ecthyma type ulcers without CVI and 10 healthy volunteers were studied. Skin biopsies for fibrinogen staining, transcutaneous oxygen tension measurements (TcPO2) and light reflexion rheography (LRR) were performed. TcPO2 readings were significantly lower in patients with CVI compared to patients of the other groups. Fibrin cuffs were found in 8 out of 16 patients with CVI, all PCT patients and 3 out of 4 ecthyma-ulcer patients. On the basis of these results we conclude that the fibrin cuff alone does not act as a barrier for oxygen transport. Fibrin cuffs in CVI are not the cause of venous ulceration but only a part of the complicated mechanism of the altered microcirculation induced by reflux in the venous macrocirculation. Fibrin cuffs are not unique for CVI but an indication of a disturbed microcirculation.