The control of plasma aldosterone during hemodialysis was investigated in 31 patients with terminal renal failure. While before hemodialysis renin predominantly influenced aldosterone, this effect dissipated during hemodialysis. In addition, no relationship was observed between changes in aldosterone and those in sodium, potassium and plasma cortisol. In a group of 10 patients isokalemic and isonatremic hemodialysis failed to document an effect sodium or potassium on hemodialysis induced changes in aldosterone. Our data suggest that none of the four factors - renin, ACTH, sodium and potassium - had constantly caused the observed changes in aldosterone during hemodialysis.