In the past, lead poisoning was recognized when classical symptoms of acute intoxication were present and the blood lead was elevated. The EDTA test is presently the most reliable method for detecting excessive lead stores. We used the EDTA lead-mobilization test to demonstrate excessive past lead absorption as a cause of renal disease in lead workers and in both gouty and hypertensive patients with renal failure. These studies show that lead nephropathy occurs in the absence of acute intoxication and that occult poisoning often goes unrecognized because of inappropriate diagnostic criteria.