Under oxidizing conditions, carotene is decolourized slowly in unsaturated and rapidly in saturated fatty esters. In unsaturated and saturated hydrocarbons, the reverse is observed. An explanation is offered based on the following hypotheses: a] That carotene is decolourized by hydrogen abstraction which upsets the entire conjugated hromophoric system and b] that the degree of internal stability of the substrate-derived peroxy-free radicals, which are the hydrogen-abstracting agencies, is inversely related to the life of carotene in that substrate. Eine Hypothese iiber die Entfarbung des Carotins d u d ein freies RadikalUnter oxydierenden Bedingungen wird das Carotin in ungesattigten Fettsaureestern langsam, in gesattigten r a s h entfarbt. In ungesattigten und gesattigten Kohlenwasserstoffen wurde das umgekehrte Verhalten beobahtet. Diese Ersdeinungen lassen sich durch folgende Hypothesen erklaren: a) Die Entfarbung des Carotins erfolgt durch Wasserstoffentzug, der das gesamte konjugierte chromophore System in Unordnung bringt und bJ der Grad der inneren Stabilitat der aus dem Substrat erhaltenen peroxydfreien Radikale, die als Wasserstoff entziehende Mittel dienen, steht mit der Lebensdauer des Carotins im betreffenden Substrat im umgekehrten Verhaltnis.Carotene dissolved in fats is known to decolourize with great rapidity under oxidizing conditions, and the process is hastened by light and heat. It was recorded long ago that the more unsaturated the fat, the greater the stability of carotene present in it 2, 3. This fact has not however been specifically accounted for in the generally-accepted theory of R. T. Holman4 that it is free radicals derived from unsaturated fatty substrates which attack the conjugated system of carotene and so destroy it by a coupled oxidation. This view is based on (a) delayed carotene destruction when antioxidants were also present in the fat systems, suggesting interception of free radicals; (b) co-oxidation of carotene with lipoxidase, a catalyst specific for the oxidation of unsaturated fatty acids containing cis nonconjugated double bonds; (c) oxidation with haematin compounds. -Carotene destruction has also been studied in hydrocarbon systems such as mineral oil5, and even used for comparing the efficiency of antioxidants E, ' . Destruction of carotene under the same experimental conditions both in fatty and in hydrocarbon substrates should enable an unified view to be developed of the mechanism involved.