The distribution of the 1 alpha,25-dihydroxycholecalciferol receptor was studied in enterocytes isolated from the upper, mid and lower villus and crypt cells of the jejunum of normal and rachitic rats. In all cell fractions a high-affinity receptor (KD congruent to 0.07 nmol/l) with a sedimentation coefficient of 3.5S was demonstrated. In normal rats there was a 60% reduction in receptor numbers in crypt cells compared with the mid and upper villous cells. Vitamin D deficiency led to a reduction in receptor numbers in all cell fractions (45% upper villus, 78% crypt cells). The data are compatible with the concept of calcium absorption occurring in the differentiated villous cells and also account for the reduction in absorption in rachitic animals.