Dietary variations (low calcium, low calcium, low phosphorus, or high strontium) change phosphate transport by the jejunum according to their respective ability to increase or block the synthesis of 1,25-dihydroxyvitamin D3, suggesting that the action of this active sterol underlies the response of intestinal phosphate absorption to vitamin D. 1,25-(OH)2D3 stimulates the active entry of Pi at the mucosal border by its action on protein synthesis. It is attractive to speculate that 1,25-(OH)2D3 might induce the synthesis of a "phosphate carrier" protein in the plasma membrane. The interpretation that the enhancement of the maximal velocity of the "phosphate pump" by vitamin D is due to the creation of new pump sites would be consistent with this hypothesis.