This study was performed to investigate the plasma levels of fibronectin in critically ill pa¬tients. Fibronectin was measured in twenty-two patients on 1 st, 3rd, 7th and 10th days of admission to the intensive care unit and it was found 33.75il.21 mg/dl., 27.47il.62 mg/dl., 37.05+1.43 mg/dl., 38.80il.43 mg/dl. respectivelly. Patients were divided into two groups as 12 in injured (Group I) and 10 patients with acute miyocardial infarctus (Group II). The plasma levels of fibronectin were found 30.78il.77 mg/dl., 22.87il.96 mg/dl., 32.83il.67 mg/dl., 35.62i2.ll mg/dl., in the first group and 37.30i0.61 mg/ dl., 32.99il.29 mg/dl., 42.12il.10 mg/dl., 42.61il.01 mg/dl., in the second on 1 st, 3 rd. 7 th 10 th days respectively. Plasma levels of fibronectin was sicnificantly decreased on 3rd day (p