The photosynthetic marine dinoflagellate,Gyrodinium resplendens, was grown axenically and harvested during logarithmic growth for analysis of its lipid-soluble pigments. Chlorophylla and 8 carotenoids were isolated from the methanol and acetone extract by column and thin-layer chromatography. Chlorophyllc was isolated by partitioning the total extract between saline aqueous acetone and hexane.Absorption spectra taken in hexane, ethanol, methanol and carbon disulfide confirm the presence of beta-carotene, peridinin, dinoxanthin and diadinoxanthin as major carotenoids.Four new minor xanthophylls are also described, one of which, namedpyrrhoxanthin, resembles an alkali-labile keto-epoxide. At least one of the minor xanthophylls occurs as an ester.Diadinoxanthin fromGyrodinium and antheraxanthin fromEuglena gracilis seem to be identical with respect to absorption curves, polarity, number of 5, 6-epoxy groups and lack of allylic hydroxyl groups; however, co-chromatography of stereoisomers after iodine-isomerization showed slight differences.Most of the carotenoids are further characterized here by their partition ratios between hexane and 95% methanol. Several of the carotenoids were tested for the presence of 5, 6-epoxy and allylic hydroxyl groups. Four of the pigments, comprising 91% of the total carotenoids are revealed as 5,6-monoepoxides by their instability toward dilute acid. One carotenoid resembles a diepoxide.