Fluoride is known to cause ectopic calcification. The biochemical mechanism(s) involved in the initiation of calcification is not understood and the accompanying ultrastructural changes remain to be elucidated. Therefore, certain relevant parameters have been investigated in the aorta of rabbits administered fluoride, 10 mg NaF/kg body wt, every 24 hr for 17 and 24 months. The significant findings are: (i) degeneration of smooth muscle fibers in the tunica media of the aorta, (ii) presence of electron-dense granules in the mitochondria and on the inner surface of the plasma membrane of smooth muscle cells, (iii) presence of matrix vesicles with electron-dense deposits, (iv) enhanced calcium content and the Ca/P ratio, and (v) increased total glycosaminoglycan (GAG) content with reduced dermatan sulfate. The presence of electron-dense granules in the mitochondria, on the plasma membrane and matrix vesicles is suggestive of the process of calcification. The enhanced calcium content as well as the Ca/P ratio supports the view that the aorta is undergoing mineralization. The total GAG is enhanced, possibly due to an increase in the content of GAGs other than isomers of chondroitin. The observation that conveys an important message is that the dermatan sulfate normally known to exist in high concentrations in soft tissues begins to decrease as the process of calcification sets in. This perhaps would hold true and may serve as an index in the process of ectopic calcification.