The author studied on the early histochemical changes of the peculiar retinal degeneration of the rabbit treated with intravenous injection of 5% solution of sodium iodate as the preceding report. The Cr-K E S (chrmo-keto-enol substance of HAMAZAKI), chief constituents of which are nucleotides of D N A, in the pigment epithelium and outer segments of rods begins to diminish gradually after 12 hrs. D N A decreases as the pigment epithelium and visual cells degenerate. In general, the Cr-K E S diminishes and disappears earlier than the Hg-K E S in the pigment epithelium and in visual cells. The authers that sodium iodate acts rather indirectly on the metabolism of the D N A and related substances in the outer layers of the retina.