IN the course of an earlier investigation into the utilization of carotene by the rat as a source of vitamin A, it was noted that there was a consistent difference between the absorption spectra of the liver non-saponifiable fractions from those rats fed vitamin A and those fed a mixture of 90 per cent beta- and 10 per cent alpha-carotene1. This difference was in the magnitude of the absorbance at 311 mµ as compared with that at 326 mµ. The alpha-ionone analogue of vitamin A was afterwards synthesized2 and the absorption maxima were found to be at 311 mµ (E1%1cm, 1,650), and 325 mµ. (E1%1cm, 1,500). This alpha-vitamin A was found to be biologically inactive but was found to be stored in the liver in the same way as vitamin A (ref. 3).