Calcium metabolism was studied in patients with diabetes mellitus. Information on the dietary intake of major nutrients was gathered from 23 non-insulin-dependent diabetic patients, 42 insulin-dependent diabetic patients and 245 nondiabetic patients under hemodialysis through a questionnaire. A calcium absorption test was performed, using an isotopic technique, in 11 non-insulin-dependent diabetic patients and 4 age-matched healthy subjects. Parathyroid function was examined, using oral phosphate loading, in 6 diabetic patients and 6 age-matched control subjects. The daily dietary intake of calcium in the non-insulin-dependent diabetic patients (602 +/- 52 mg) was up to the average daily nutritional requirement (600 mg). The calcium absorption rate in these patients (54.4 +/- 13.9%) was similar to that in the healthy subjects (50.1 +/- 5.4%). The response of parathyroid hormone to phosphate loading was significantly reduced in the diabetic patients compared to the control subjects. The results suggest that calcium homeostasis in diabetic patients with normal renal function is almost conserved, despite the decreased response of parathyroid hormone to phosphate loading.