Catalysis by iodine and light of the aerobic oxidation of carotenoids containing allylic hydroxyl groups to the corresponding ketones is reported. Molecular oxygen (air) can with advantage be replaced by p- chloranil as oxidant, and the catalytic effect of iodine and light on the allylic oxidation with p-chloranil is demonstrated. Illumination by means of standardized artificial light is the method of choice. On exposure to artificial Na-light the production of undesirable side-products was suppressed, and a nearly quantitative yield of keto-products was obtained. The method has been employed for the partial synthesis of 4-hydroxy-4[image]-keto-[beta]-carotene (IV) from isozeaxanthin (III), and compound (IV) has been characterized.