Chromatium strain D was grown on autotrophic medium with sulfide as the sole electron donor and on heterotrophic media. The following growth parameters were monitored: sulfide, intracellular sulfur, cell number, bacteriochlorophyll, protein, storage polysaccharide, dry weight, and turbidity. In addition, electron micrographs of the bacteria at each stage of growth were prepared. The metabolism and structure of the bacteria were found to be dependent on whether sulfide or sulfur was the primary photosynthetic electron donor during growth as autotrophs. The major effects in shifting from sulfide to sulfur were noted as cessation of bacteriochlorophyll synthesis, decreased cellular protein content, and increased rate of cell division. Such effects were not seen in heterotrophic growth on succinate.