The fine structure of the phototrophic sulfur bacterium Chromatium buderi was studied in ultrathin sections and freeze-etch preparations. In addition to an intracytoplasmic membrane system common to all species of the Chromatiaceae, C. buderi contained extended lamellar membrane structures possibly due to too high light intensities during growth. The cell wall of C. buderi was found to be covered by a honeycomb-like outer layer consisting of macromolecular “wine-glass” shaped subunits 60–80 nm by 60 nm in size. This outer cell wall layer appears to be a typical property of the large cell Chromatium species.