Plasma aluminium, zinc and copper were determined in 68 patients with chronic renal insufficiency and in 20 healthy individuals. In the renal insufficiency group 16 patients had received aluminium containing substances particularly phosphate binding drugs (aluminium hydroxide) for a long time. We observed that only the patients taking aluminium hydroxide showed elevated aluminium levels in plasma (controls: 0.86 +/- 0.27 mumoles/l; renal insufficiency: 3.05 +/- 1.63 mumoles/l). In two of these patients with symptoms of "dialysis dementia", plasma aluminium concentrations were markedly increased. The zinc concentrations in plasma of patients with renal insufficiency were slightly decreased (controls: 14.48 +/- 2.65 mumoles/l; renal insufficiency: 11.77 +/- 2.35 mumoles/l); the plasma copper concentrations were slightly increased (controls: 17.3 +/- 2.83 mumoles/l; renal insufficiency: 22.98 +/- 4.7 mumoles/l). There was a distinct decrease of plasma zinc concentrations in patients with raised aluminium levels. The clinical aspects of these changes are discussed.