The anaerobic, photosynthetic bacterium Chlorobium thiosulfatophilum utilizes CO2 as its carbon source and operates at the mesophilic temperature of 30 degrees C. It requires incandescent light for growth and compounds such as H2S, S degrees, S2O32-, Or H-2 as a source of electrons. Of these compounds, H2S as sulfide is the preferred electron donor, with other compounds utilized only when sulfide has been depleted from the medium. The organism is also capable of indirectly utilizing carbonyl sulfide (COS), since COS reacts with water to form CO2 and H2S. This work presents kinetic information on the rate of growth of C. thiosulfatophilum, as well as the rates of uptake of both H2S and COS. The growth is dependent on light intensity according to a Monod type relationship.