Hypertension, anemia, and arteriovenous shunts represent very important pathogenic factors in the occurrence of cardiovascular morbidity and mortality in patients with chronic renal failure. It can be expected that endothelin (ET), the most potent vasoconstrictor known at present, can react in a significant way to the hemodynamic changes caused by the construction of a vascular shunt or anemia. In 14 patients the plasma ET concentration was examined before and 24 and 7 days after the construction of arteriovenous fistula. In 27 patients undergoing chronic hemodialysis treatment, ET was examined before the erythropoietin (EPO) therapy and after 2 months of EPO therapy, when partial correction of anemia had been achieved. The construction of arteriovenous fistula by itself had no significant influence on the plasma ET concentration. Subcutaneous application of EPO in doses that led to gradual correction of anemia was not accompanied by the rise of plasma ET. The average plasma concentration of ET was significantly higher in hemodialyzed patients, when compared to healthy controls as well as to patients with chronic renal failure before hemodialysis treatment was started.