RETINENE1, first noted by Wald in his work on the visual-purple cycle, is the aldehyde of vitamin A1, from which it has been prepared in high purity2. Retinene2, the corresponding aldehyde of vitamin A2, enters into the porphyropsin cycle of freshwater fish retinas. It has been obtained by fractionation of the aldehydes prepared from a mixture of vitamins A1 and A2 derived from ling-cod liver oil3. As described by Wald, retinene2 shows λmax. 405 mµ in chloroform) and 705 mµ in the antimony trichloride colour test. The preparation obtained by oxidation of vitamin A2 by means of manganese dioxide shows λmax. 405 mµ (chloroform), 385 mµ (cyclohexane), and 720 mµ (antimony trichloride test) fading to 705 mµ.