Rats were injected intraperitoneally with cadmium chloride (5 or 10 mg/kg body weight) and calcium chloride (50 mg/kg body weight) simultaneously. Rats were killed after 2 hours. The accumulation of cadmium and calcium in the liver and kidney, and in liver and kidney mitochondria was examined. The mutual effect of cadmium and calcium on the respiration of the mitochondria was also investigated. The results were as follows: 1) concentrations of cadmium in the liver were lower in the presence of calcium than in its absence, but the accumulation of cadmium was marked. 2) concentrations of cadmium in liver mitochondria were lower in the presence of calcium than in its absence. 3) the decrease in respiratory control index and ADP/O ratio of liver mitochondria was lower in the presence of calcium than in its absence. 4) the same statements are true for kidney and kidney mitochondria. 5) The concentrations of calcium in the liver and kidney in the presence of both cadmium and calcium were similar to the those when calcium was absence.