The uptake and release of 45Ca from the rat intestinal mucosal epithelium were investigated under a variety of conditions. The initial rate of uptake characterized a calcium pool with a half time of saturation of less than 2 min. The entry of 45Ca into this pool was inhibited by NaCN and ethacrynic acid and was stimulated by the removal of Cl- from the incubation. The initial rate of 45Ca release was also inhibited by NaCN and removal of Na+ from the incubation. Parathyroid hormone administration enhanced the release of 45Ca from cells prepared from parathyroidectomized animals. These observations suggest that calcium transport across the brush border and basal lateral membranes are identifiable components of the kinetics of 45Ca uptake and release and that parathyroid hormone stimulates a sodium dependent mechanism of calcium transport across the basal lateral membranes.