To study the effect on plasma 25-hydroxycholecalciferol (25(OH)D), 1, 25-dihydroxycholecalciferol (1, 25(OH)(2)D) and parathyroid hormone (PTH) we supplemented premenopausal (aged 30 (so 7) years) and postmenopausal (aged 61 (so 2) years) white women living in The Netherlands in late winter/early spring, and elderly black and white women (aged 75 (so 6) years) living in Curacao (Dutch Antilles) with either 10 or 20 mu g cholecalciferol/d for 4, 5 and 9 weeks respectively, Baseline plasma 25(OH)D concentration of Dutch women was lower than that of Curacao women, Postmenopausal Dutch women had a higher PTH concentration in plasma than premenopausal Dutch and postmenopausal Curacao women, There were no differences in plasma 1,25(OH),D, Cholecalciferol administration increased 25(OH)D in all groups, 1, 25(OH),D in postmenopausal Curacao women and PTH in postmenopausal Curacao women and premenopausal Dutch women, Serum and urinary Ca and phosphate concentrations did not change, There were no response differences between 10 and 20 mu g doses, Oral cholecalciferol administration (either 10 or 20 mu g/d) to women living at northern latitudes in late winter/early spring increased 25(OH)D levels to the baseline levels of elderly people living in the tropics.