Surprisingly, neither the precise pharmacological effect nor the toxicological profile is usually established for food components. Carotenoids are no exception in this regard. Only limited insight into the pharmacology and toxicology of carotenoids exists. It is known that the antioxidant action of carotenoids is determined by 1. electron transfer reactions and the stability of the antioxidant free radical, 2. the interplay with other antioxidants and 3. the reaction with active oxygen. Numerous metabolites of carotenoids are formed upon their action as an antioxidant. Most of these metabolites have an unknown biological activity. It is concluded that a severe lack of knowledge hampers adequate suggestions for human supplementation.