The distribution and the concentration of quinones in 5 species of photosynthetic bacteria and 4 species of algae were investigated. The Athiorhodaceae, except for Rhodospirillum rubrum, contained ubiquinone as the major quinone component. Rhodospirillum rubrum contained two kinds of quinones, i.e. ubiquinone and rhodoquinone. Chromatium, strain D contained two kinds of quinones, i. e. ubiquinone and vitamin K2. The green sulfur bacterium, Chloropseudomonas ethylicum, contained vitamin K2 and a Chlorobium quinone-like substance. The marine algae tested, Porphyra yezoensis, Porphyra sp. and Hizikia fusiforme, contained vitamin K1, plastoquinone A, α-tocopherylquinone and ubiquinone. In Chondrus ocellatus, the presence of a ubichromenol-like substance was detected instead of ubiquinone. Other types of plastoquinone and tocopherylquinone were not found in these algae. In the thalli of Porphyra sp., vitamin K1, plastoquinone A and α-tocopherylquinone were found to be localized in chloroplasts.