The effect of hemodialysis on plasma norepinephrine (NE), epinephrine, and dopamine levels was studied in 11 patients undergoing maintenance hemodialysis. The results showed that the baseline plasma concentrations of NE and dopamine were significantly elevated in patients with end-stage renal disease undergoing maintenance hemodialysis. Intradialysis weight loss and fall in the serum glucose concentration during dialysis correlated with changes in plasma epinephrine and NE concentrations. Single-pass dialysis resulted in a marked reduction in the plasma NE concentration, indicating significant removal by dialysis. These observations should be taken into consideration when interpreting plasma catecholamine data obtained in the course of investigation of hypertensive patients with end-stage renal disease.