Newer methods of microscopy promise to provide a better insight into the physicochemical aspects of tissue structure than has been attained by conventional technics. An exploratory investigation is reported of the ultraviolet absorptive behavior of renal arterioles and arteries, employing the Polaroid color-translating ultraviolet microscope. In the arteriolar necrosis accompanying malignant hypertension and renal periarteritis nodosa changes of particular interest were observed.