The content of collagen in the bone tissue of rats and incorporation of 14C from 2-14C-glycin into it were studied as affected by vitamin D deficiency. It is established that under experimental rachitis intensity of the radioactive label incorporation into soluble collagen is 1.7 times as low as in the norm. A decrease in the amount of the collagen soluble fraction and accumulation of its insoluble fraction and distribution of radioactivity in these fractions might evidence for rapid "ripening" of soluble collagen in the rats with D-hypovitaminosis.