The aim of the present study was to compare the bioavailability of calcium from calcium carbonate and milk and to investigate if 1,200 IU of cholecalciferol a day increased intestinal absorption of calcium. Both young women and a group of older persons of both sexes were included to study the influence of age and sex. In total, 53 healthy women and men were included: a group of 23 younger women (median age 30) and an older group of 15 women and 15 men (median age 66). The study period was 4 weeks; each participant completed four treatment regimens randomly: CaCO(3), CaCO(3 )+ 1,200 IU of cholecalciferol, milk, and placebo. All regimens were distributed three times a day and consisted of 1,200 mg of elementary calcium. The 24-hour urine calcium excretion was used as a method. Total urinary calcium excretion rates (mmol/day) were as follows (mean +/- SD): placebo 4.41 +/- 2.17, milk 5.17 +/- 2.33, CaCO(3) 5.83 +/- 2.03, and CaCO(3 )+ D 6.06 +/- 2.46. All regimens compared to placebo were significant. Addition of cholecalciferol to the CaCO(3) regimen increased calcium excretion but insignificantly: 0.27 +/- 2.84 mmol/day. The increase in calcium excretion during the milk regimen was significant only for the old group: 0.96 vs. 0.28 mmol/day. No other difference was found according to age and sex. The bioavailability of calcium carbonate and milk was demonstrated. Additional cholecalciferol (1,200 IU) to individuals in positive calcium balance with serum 25(OH)D levels >50 nmol/L only marginally increased calcium absorption in a short-term intervention.