The availability of currently used methods of measuring intestinal calcium absorption is limited by their expense and complexity. Since this measurement may be important in selecting appropriate therapies for patients with osteoporosis, a simpler procedure is required. This paper describes a test which measures the intestinal absorption of stable strontium. A comparison of this test with the single-isotope radio-calcium absorption test in the same group of patients showed a close correlation between the fractional absorption rates of the two elements (r = 0.93, P less than 0.001). Subjects were correctly categorized as having normal or low absorption in 12 out of 13 cases (92%) and the value in the misclassified subject was at the borderline between normal and low calcium absorption. The convenience, low cost, and freedom from radioactivity of stable strontium make it suitable for routine clinical use and, if necessary, repeated testing. If these early results are confirmed, this test will make the assessment of calcium absorption much more widely available.