Arterial specimens from the radial artery were removed in connection with Brescia fistula operations on 15 uraemic patients and were studied by light and electron microscopy. The patients lacked clinical signs of arterial insufficiency. Radial artery specimens from 15 humans that underwent forensic post-mortem examination served as controls. The intima of the uraemic patients was significantly thicker than that of the controls. In 8 of the uraemic arteries light microscopy disclosed necrotic areas in the media and in 2 cases such areas in the intima, compared to only one case with patchy medial necrosis in the controls. Calcification was histochemically demonstrated in 6 of the uraemic arteries while none of the controls showed this change. The presence of degenerated and necrotic smooth-muscle cells was verified at the ultrastructural level. Furthermore, modified smooth-muscle cells appeared in the intima and the media and were probably of significance for the synthesis of the increased amounts of collagen and mucopolysaccharides that could be demonstrated. Ultrastructurally evidence of calcification could be demonstrated in the internal elastic membrane and in necrotic areas in the intima and the media. In the latter localization the calcification process seemed to start in relation to extracellular vesicular structures, probably representing cell debris. The possible significance of the observed changes for the development of symptom-giving arterial disease is discussed.