We examined intact PTH and 1,25-dihydroxyvitamin D [1,25-(OH)2D] in both baseline and dynamic conditions (low calcium diet) in 14 patients with Turner's syndrome (mean age, 12.6 +/- 5.9 yr; range, 4.2-21.0 yr) and bone demineralization as well as in a control group of 15 healthy girls (mean age, 12.8 +/- 5.6 yr; range, 3.8-22.7 yr). In both groups we also measured osteocalcin serum levels in response to oral 1,25-(OH)2D3 administration (1.8 micrograms/m2/daily for 6 days) to assess osteoblast function. The low calcium diet decreased ionized calcium (Ca2+) levels and elevated PTH values to the same extent in both patients (Ca2+, -8.40 +/- 3.78%; intact PTH, +47.88 +/- 13.24%) and controls (Ca2+, -9.09 +/- 3.25%; intact PTH, +52.77 +/- 10.52%; P = NS vs. patients). While controls showed an increment in their serum 1,25-(OH)2D levels (+52.15 +/- 8.95%), patients did not (+10.93 +/- 4.71%; P = NS vs. baseline; P < 0.001 vs. controls). 1,25-(OH)2D3 administration caused a rise in the serum osteocalcin levels in a similar fashion in both groups (peak values: patients, +35.38 +/- 7.20%; controls, +34.09 +/- 7.98%; P = NS). We conclude that in patients with Turner's syndrome there is an altered renal vitamin D metabolism in response to physiological stimulus, while osteoblast function in response to 1,25-(OH)2D3 administration is not affected.