<jats:p>The pigments of the recently isolated marine prochlorophyte <jats:italic>Prochlorococcus marinus</jats:italic> were characterized by modern chromatographic and spectroscopic analysis. The major photosynthetic pigment is 8‐desethyl, 8‐vinyl chlorophyll <jats:italic>a</jats:italic>. Accessory pigments are 8‐desethyl, 8‐vinyl chlorophyll <jats:italic>b</jats:italic>, zeaxanthin, <jats:italic>α</jats:italic>‐carotene, an unknown carotenoid, and possibly Mg 3,8 divinyl‐pheoporphyrin <jats:italic>a</jats:italic><jats:sub>5</jats:sub><jats:italic>.</jats:italic> Chl <jats:italic>a</jats:italic> is not present in this organism. <jats:italic>P. marinus</jats:italic> is the first wild‐type oxygenic phototroph that does not have Chl <jats:italic>a</jats:italic> as its major photosynthetic pigment and it is the only procaryote <jats:italic>∊</jats:italic>‐cyclic carotenoids (<jats:italic>α</jats:italic>‐carotene). <jats:italic>P. marinus</jats:italic> 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.