Recent interest in the role of oral calcium carbonate and low calcium dialysate has emphasised the need for a simple, safe and inexpensive test of intestinal calcium absorption. The stable, non-radioactive, strontium absorption test fits these requirements. Stable strontium and calcium-45 were administered simultaneously to 19 fasting CAPD patients and their serum levels were subsequently measured. There was a close correlation between the absorption of calcium and strontium at both 60 and 120 min post-ingestion. The two markers resulted in the same classification of patients as normal or malabsorbers in 18 of 19 cases (95%), suggesting that strontium could be substituted for calcium-45 in a 60-min test of absorption enabling safe, simple and repeated measurements in renal failure patients.