A comparison was made of the amount and crystallinity of mineral deposited in the course of the arteriosclerosis in arterial walls in diabetic patients and in individuals with normal carbohydrate metabolism. The macroscopically unchanged tunica intima, fibro-lipidic plaques and bone-like lamellae were taken from aorta thoracalis , aorta abdominalis, arteriae femorales and arteriae coronariae in the course of the autopsy of 17 insulin dependent diabetic individuals and of 9 persons with arteriosclerosis, but with normal carbohydrate metabolism, called control group. The total inorganic constituents in the three kinds of samples were determined by ashing of dried samples at 600 degrees C for 6 h. Crystallinity of mineral was defined as the ratio of the spins connected with the radiation-induced stable paramagnetic centers present in the crystalline lattice of hydroxyapatite crystal, to the total ash content of the sample. An increase in the amount and in the crystallinity of deposited mineral was observed when consecutive stadia of development of arteriosclerotic lesions were compared. This phenomenon resembles the maturation of mineral observed in the course of bone development.