The appearance of a polar metabolite of 25-hydroxychotecalciferol has been studied in the intestinal mucosas of nephrectomized rats and rats which have been made uremic by ureter ligation. In confirmation of previous work by Fraser and Kodicek, it was found that nephrectomy prevents the appearance of this metabolite in the intestine. On the other hand, equivalent amounts of the metabolite were found in uremic rats and in sham-operated controls, showing that the production of this metabolite is independent of the uremic state of the animals. In addition, it was shown that the metabolite produced in vitro by kidney homogenates is identical to that found in vivo in the intestine.