Keeping rats on a ration with a 1:3 proportion of calcium and phosphorus for 2 weeks results in hyperprosphatemia, hypocalcemia and renal calcinosis with uremia. When putting these animals on a food ration with the calcium and phosphorus ratio of 1:1 the concentration of these elements in the blood quickly returns back to normal, while renal calcinosis continues for the whole period of observation (7 months). The growing animals are more sensitive to a phosphorus excess than are the adult ones. An excessive consumption of phosphorus leads to its increased excretion with the urine with concurrent diminution of the calcium excretion. The blood and urine pH then experiences no change, whereas the ability of the turned inside out segments of the small intestine to absorb calcium as against the concentration gradient (active transport) in vitro not only does not diminish, but initially even goes up. It is suggested that the excess phosphorus content in the food ration tends to directly derange absorption of calcium in the intestines, this resulting in the development of hypocalciemia, hyperparathyroidism and calcinosis of the viscera and tissues.