Monoalgally cultured Thoracosphaera heimii contained chlorophyll a, chlorophyll c, β,β-carotene, echinenone, canthaxanthin, diadinoxanthin, diatoxanthin, dinoxanthin, pyrrhoxanthin, peridinin, peridininol, the structurally unknown glycoside P-457 and an unidentified acetylenic xanthophyll. Echinenone and canthaxanthin are reported from monoalgal material of dinoflagellates for the first time. The diatoxanthin-diadinoxanthin fraction consisted of six xanthophylls which have been separated on alkaline TLC plates without prior chemical derivatization, and spectrometrically characterized in their native state. Spectrometric data for the polar, minor xanthophyll peridininol, including first record of the ¹H NMR spectrum, are presented. The carotenoid complement, notably the C37-sketetoned peridinin, peridininol and pyrrhoxanthin and the structurally unknown P-457, supports that T. heimii is a member of the Dinophyceae and not the Prymnesiophyceae.