The effects of selective parathyroidectomy on the adaptation to a low calcium intake were studied in one‐year‐old male rats. Parathyroidectomized animals showed increased net absorption of intestinal calcium compared to that of intact animals both at a normal and at a low intake of dietary calcium. The difference was highly significant on the low level of dietary calcium. In the parathyroidectomized animals, significantly higher values were found in the group of rats fed the low calcium diet than in those supplied the calcium supplemented diet. Urinary calcium excretion was reduced because of the reduced plasma calcium level. While there was no disturbance of intestinal calcium absorption, selective parathyroidectomy resulted in a reduced ability to mobilize skeletal calcium as shown in a previous study. This was found to be necessary for the adaptation to a low calcium intake in the adult ani