In a prospective study levels of interleukin-2 receptors (Il-2-R) in serum and of endothelin (ET) in plasma were sequentially determined in 97 patients (39 women, 58 men) before and after liver transplantation (Ltx). The aim of the study was no evaluate the correlation and the time course of these two parameters after Ltx. The postoperative levels of Il-2-R and ET were higher in transplant recipients with no postoperative complications than in patients who had undergone operations to the liver. Patients suffering from acute rejection episodes after transplantation had more markedly increased Il-2-R and ET levels than those with an uneventful course, and this persisted for 3 months. A significant rise of Il-2-R concentrations 3-6 days before a biopsy confirmed rejection proved to have a sensitivity of 68% and a specificity of 68% respectively. A corresponding ET increase preceded rejection episodes confirmed by biopsy with a sensitivity of 62% and a specificity of 67%, respectively. These laboratory data can be obtained daily: they cannot undermine the "gold standard" of liver biopsy, but they are extremely beneficial in determining the timing and indication for the liver biopsy.