Ultraviolet B radiation decidedly influences the synthesis of vitamin D and therefore mineral and bone metabolism. It must also be taken into account that a normal unsupplemented diet is usually deficient in this vitamin. Two groups of subjects pertaining to the Spanish Antarctic Expedition 1988-1989 were studied to determine whether special conditions of irradiation and solar exposure found in Antarctica induce alterations in the abovementioned metabolism.Each group consisted of 11 healthy males with ingestion of less than 500 mg/day of calcium. The second group was administered vitamin D3 supplements of 1,000 UI/day. Two blood samples were performed at an interval of 22 days during the Antarctic summer to determine calcium, phosphorus, magnesium, parathormone (PTH) and 25-hydroxycholecalciferol [25(OH)D].Neither group varied in calcemia, phosphoremia or magnesemia. In the first group the 25(OH)D decreased markedly (p less than 0.01) with no variations being observed in PTH. In the supplemented group, and insignificant increase of 25(OH)D was observed which was significant enough to cause a marked decrease in PTH (p less than 0.01).Subjects passing periods of time in Antarctica should receive vitamin D3 supplementation at doses less than 1,000 UI/day.