The role of renal nerves and endothelins, acting at ET(A) receptors, in the regulation of renal excretory function was investigated in male Long-Evans rats. Catheters were placed in the femoral vein for fluid and drug infusion, in the femoral artery for blood pressure recording as well as in the bladder for urine collection. Infusion of 16.4 nmol/kg/min of the ET(A) receptor antagonist BQ-123 for 50 min was performed in freely moving, intact and renal denervated rats. As a result of BQ- 123 infusion, urine flow rate diminished (P < 0.02) and Uosm increased (P < 0.05) in the intact rats, but not in the renal denervated rats. Bilateral renal denervation itself as well as ET(A) receptor inhibition in both intact and renal denervated rats did not change the mean arterial pressure, heart rate, or the excretion of sodium, potassium and chloride. The data obtained suggest an interrelationship between renal nerves and endothelin-A receptors in the regulation of renal water excretion.