The carotenoids of the Vaucheriales Vaucheria and Botrydium have been investigated. Both contain the same pigments β-carotene, cryptoxanthinepoxid (traces), zeaxanthin (traces), antheraxanthin, a new xanthophyll named vaucheriaxanthin with three esterified hydroxyls and another unknown pigment. The carotenoids of the Vaucheriales seem to be not identical with the carotenoids of the other Xanthophyceae investigated by THOMAS and GOODWIN 8. The identity of pigment composition of Vaucheria and Botrydium underlies their close relationship in the algal system. The significance of these pigments is discussed. Diatoxanthin, a pigment of diatoms, is identical with antheraxanthin.