Intestinal mucosal cell turnover was studied in vitamin D-deficient rats in response to vitamin D3 repletion. Four hours after a single oral dose of 100 U of vitamin D3, 3H-thymidine incorporation into deoxyribonucleic acid was enhanced. Mucosal cell migration rate of the vitamin D-repleted animals was 1.5 times that of the deficient animals. The accelerated mucosal cell turnover was associated with an increase of approximately 20% in villus height. This stimulation of mucosal cell proliferation preceded enhanced calcium transport, and, therefore, may be an important component of action of vitamin D on the intestine.