Studies on the relative efficiency of lactose fermentation by lactose-fermenting yeasts were conducted and Torula cremoris no. 2 was selected as the most efficient organism for semi-plant expts. with 150-gallon batches of whey. The optimal operating temp. for the fermentation in the semi-plant was found to be 33-34 [degree]C. Yeast equivalent to 2% of the wt. of the lactose ensured satisfactory fermentation. The effects of the initial pH of the whey and the course of pH change during the fermentation on the rate of fermentation were investigated and a range of 4.7 to 5 was found to be satisfactory. Yields of 90.73% of the lactose as alcohol were obtained in the laboratory. In the semi-plant, yields as low as 84% were obtained. The equipment and operation of a plant producing alcohol from whey are described. The relative economy of the process is discussed.