The authors study mechanisms of nephrotoxic action of high-osmolar radiopaque substance (RPS) and the role of endothelin-1, hormonal endothelial factor, in these mechanisms in patients with different variants of chronic glomerulonephritis. Endothelin-1 is a potent endogenic vasoconstrictor participating in regulation of intrarenal hemodynamics and renal function the synthesis of which id related to Ca metabolism. Mechanisms of nephrotoxic action of RPS involve disturbances of Ca metabolism (hypercalcemia), high concentration of blood endothelin-1 which directly correlated with baseline creatinine in the serum and deterioration of renal function after RPS introduction. Ca ions antagonists (corinfar) contribute to prevention of changes in endothelin-1 synthesis relevant renal dysfunction induced by RPS.