The purple sulfur bacteria Thiocapsa roseopersicina, strains BBS and SL-4, and Lamprobacter modestohalophilus assimilate glycerol when grown in the light under the anaerobic conditions or in the dark under the aerobic conditions. Apart from glycerol, the bacteria require for their growth reduced sulfur compounds (thiosulfate) and bicarbonate. The 14C from 1-14C-glycerol is incorporated into the cells of T. roseopersicina and L. modestohalophilus at a lower rate in the presence of thiosulfate under the phototrophic conditions. In the presence of glycerol, all the studied purple sulfur bacteria produce more reserve carbohydrates of the glucan type than on the mineral medium. Glycerol metabolism in purple sulfur bacteria, like that in nonsulfur purple bacteria, involves glycerokinase and the pyridine nucleotide independent alpha-glycerophosphate dehydrogenase. The activity of these enzymes does not depend on the conditions of the cultural growth and the presence of glycerol in the medium.