SUMMARY: The synthesis of cellulose by Acetobacter on media based on blackstrap molasses was studied. Methods are described for the determination of cellulose, and of growth as cell-N, in static culture. Different carbohydrate, substrates were compared for cellulose production by Acetobacter acetigenum strain EA-I: hydrolysed molasses was found to give the largest yields. In media based on this substrate growth and cellulose production both reached their maximum values with a sugar concentration of 7·9% (w/v) after 40 days' growth at 26--29°. The maximum conversion (18%) of sugar to cellulose, however, was obtained with 1·5% (w/v) sugar. Cellulose synthesis ceased when growth stopped, even when the sugar in the medium was not exhausted, indicating that cellulose was synthesized only by the actively growing organism. The cellulose produced/mg. cell-N and % cellulose in the pellicles decreased with increased sugar concentration in the medium. Other Acetobacter strains were examined in this medium; the cellulose yields varied over a wide range, equivalent to conversions of 1·9--23·%.