1. The fermentation of poultry manure in an attempt to increase its value for poultry diets was studied. 2. Microbial strains for the efficient elimination of uric acid were isolated. 3. Suitable, cheap carbon sources (methanol, glycerol, glucose) were tested in attempts to increase cell yield. 4. These criteria were used to study the 41 bacterial and 8 yeast strains which were the most prolific on slants and which were isolated from experiments with a shaker. A strain was selected for experimentation with a fermentor. 5. Fermentor experiments were done on a laboratory scale (101) and in a non‐sterile semicontinuous system (150 1), cell mass production being similar in both systems.