The pigments of the recently isolated marine prochlorophyte Prochlorococcus marinus were characterized by modern chromatographic and spectroscopic analysis. The major photosynthetic pigment is 8‐desethyl, 8‐vinyl chlorophyll a. Accessory pigments are 8‐desethyl, 8‐vinyl chlorophyll b, zeaxanthin, α‐carotene, an unknown carotenoid, and possibly Mg 3,8 divinyl‐pheoporphyrin a5. Chl a is not present in this organism. P. marinus is the first wild‐type oxygenic phototroph that does not have Chl a as its major photosynthetic pigment and it is the only procaryote ∊‐cyclic carotenoids (α‐carotene). P. marinus demonstrates a range of biosynthetic abilities that will necessitate a re‐evaluation of the evolution of chlorophyll and carotenoid biosynthesis in pro‐ and eucaryotic phototrophs.