The residue from centrifugation of cow and poultry manures which have been digested anaerobically contain, respectively, 10.2 and 31% of their dry weights as protein. The supernatant fluids contain high concentrations of acetic, propionic, and butyric acids. A mixed culture of photosynthetic bacteria grow on substrates in these liquids when exposed to light. The cell yields as protein are 20 and 24%, respectively, of the dry weight of dry cow and chicken manure. The total production of protein resulting from anaerobic fermentation and growth of photosynthetic bacteria is 30.2% of the dry weight of cow manure, 55% of the dry weight of chicken manure.