Male rats of the Wistar strain (6 weeks old) were divided into 2 groups; control group and experimental group. The control group was fed a cadmium-free diet. The experimental group was fed a diet containing 100 ppm of cadmium (CdCl2). During the 33-day period of cadmium intake, body weight was recorded. For the 7th to 10th, 16th to 19th, and 25th to 28th day of the experimental period, food consumption was recorded and at the same time urine and feces were sampled to obtain the calcium and phosphorus concentrations. On the 8th, 17th, and 26th day, about 0.2 ml of blood was sampled to determine the calcium and phosphorus concentration. The concentration of calcium remained stationary during the experimental period, but the concentration of phosphorus in the experimental group was significantly lower than that in the control group. On the 29th or 30th day 45Ca(1 muCi) was given orally with the cold calcium, and the 1- and 2-hr blood was collected by heart puncture to obtain the 45Ca activity in the serum. The 1-hr activity in the control group was significantly higher than that in the experimental group. On the final day, the rats were sacrificed to obtain the duodenum and kidney calcium-binding protein. The binding activities of these proteins in the experimental group were significantly lower than that in the control group.