In inflammatory processes endothelin exerts an important effect on the pancreatic blood vessels and disturbances in pancreatic microcirculation. The aim of the study was to evaluate the usefulness of plasma endothelin-1 (ET-1) levels in determining the severity of pancreatitis, its prognosis and monitoring the course of therapy. The investigations were carried out on 115 subjects: 85 patients with pancreatitis and 30 persons serving as a control group. All the participants' ET-1 levels were determined by means of an enzymoimmunological test (Endothelin ETA Kit, Catalog No:583151, Cayman Chemical Company, Michigan, USA) on the 1st, 3rd, 5th and 7th days of treatment. In the control group, the mean ET-1 level was 1.37 pg/ml. Acute pancreatitis (AP) was diagnosed in 53 patients, including 36 patients (67.9%) with severe AP. Their Ranson's scores were over 3 points. The highest mean plasma ET-1 levels were observed in 10 patients with severe AP with necrosis (6.37 +/- 1.9pg/ml). (5 to 9 points on Ranson's scale). In 26 patients with severe AP without necrosis, the mean plasma ET-1 level was 3.49 +/- 1.24 pg/ml. In 17 patients with mild AP the mean plasma ET-1 level was 3.48 +/-1.16 pg/ml (3 to 4 points on Ranson's scale). ET-1 levels normalized gradually with successful treatment. An increase in ET-1 levels between the 5th and 7th days was an unfavorable prognostic factor that was observed in all the patients who died. Measuring plasma ET-1 levels permits early determination of cases with severe AP. ET-1 can be used as a marker for both the progress of the disease and the efficacy of the treatment. An increase in plasma ET-1 level between the 5th and 7th days of treatment may indicate irreversible ischemic lesions in the pancreas and the development of necrotic lesions.