Plasma aluminum levels were measured in 17 children with chronic renal failure who were receiving aluminum containing antacids for the control of hyperphosphatemia. Seven children were on hemodialysis, five on peritoneal dialysis, and five were awaiting dialysis with creatinine clearances between 10 to 20 cc/min/1.73 m2. Plasma aluminum levels correlated directly with oral aluminum dosage; extremely high levels were documented in small, nondialyzed children. Bone aluminum levels were measured in four children with high plasma levels and confirmed significant aluminum loading. Other factors such as the level of aluminum in dialysate and tap water were measured and were not contributory. All patients with plasma aluminum levels greater than 100 micrograms/liter had signs of aluminum toxicity and were receiving greater than 75 mg/kg/day of elemental aluminum orally. We concluded that children who require greater than 30 mg/kg/day of elemental aluminum to control hyperphosphatemia should have plasma aluminum levels monitored and/or be considered for other forms of therapy including more restricted diets and earlier or more aggressive dialysis.