1. The distribution of the 1α,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.
2. In all cell fractions a high-affinity receptor (KD ⋍ 0.07 nmol/l) with a sedimentation coefficient of 3.5S was demonstrated.
3. In normal rats there was a 60% reduction in receptor numbers in crypt cells compared with the mid and upper villous cells.
4. Vitamin D deficiency led to a reduction in receptor numbers in all cell fractions (45% upper villus, 78% crypt cells).
5. 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.