THE growth of autotropic unicellular organisms in purely inorganic medium is of great interest in biological studies. The production of amino-acids by such organisms is intimately connected with this growth. In the case of unicellular green algæ, the production of amino-acids have been investigated by Fowden1, Pearsall and Fogg2 and Eny 3. I have attempted to determine the free and bound amino-acids produced in the photosynthetic red sulphur bacteria using the technique of paper chromatography. These experiments also furnish a comparative study of the protein units of algæ and photosynthetic bacteria. © 1959 Nature Publishing Group.