The carotenoids of selected Cryptophyceae, Rhodomonas D3 and Cryptomonas ovate, have been examined by methods including HPLC, mass spectrometry ¹H NMR and circular dichroism 3"R,6'R-Chirality has been assigned to monadoxanthin from ¹H NMR and CD data; β,ε-carotene possessed the common 6'R-chirality. The quantitative distribution pattern of carotenoids in Cryptophyceae established here and previously, totalling five species' is discussed in chemosystematic context. β,ε-carotene (3-8% of total) is the major carotene, accompanied by ε,ε-carotene (0-2%), β,β-carotene (0-1%) and lycopene (0-trace). Zeaxanthin (2%) was identified in C. ovate. The diacetylenic alloxanthin is the major carotenoid (70-88%), and the monoacetylenic crocoxanthin (5-15%) and monadoxanthin (0-16%) less abundant. No epoxidic or allenic carotenoids could be detected. The biosynthetic precursor of acetylenic carotenoids in this primitive algae class is discussed. The significance of Cryptophyceae in the marine food chain is commented on, using alloxanthin as an indicator.