We analyzed multiple trace elements in tap water, dialysis fluids, and CSF of patients on dialysis and with chronic renal insufficiency. Before placement of a deionizer in the dialysis unit, we found elevated levels of aluminum, barium, copper, silicon, and zinc in tap water and dialysis fluids. These were corrected by the deionizer. CSF silicon content was increased in patients with chronic renal insufficiency and on dialysis; CSF aluminum, barium, copper, and zinc were normal.