SUMMARY: Y(glucose) values for Lactobacillus plantarum, L. delbrueckii, L. casei, L. lactis and L. bulgaricus, grown as batch cultures in defined medium, and L. casei, grown in complex medium, were 20.0 to 33.3.Y(galactose) values for L. plantarum were 25.7 to 32.5. Each species produced acetate in addition to lactate, and Y(ATP) values, corrected for the energy produced simultaneously with the formation of acetate, were 10.0 to 10.9, close to 10.5, proposed as a standard value by Bauchop & Elsden (1960). Neither formate nor ethanol was produced in more than trace quantities. Y(glucose) values determined for L. lactis and L. bulgaricus at 40 °C were less than 50% of those determined at 37 °C. Production of lactate and acetate accounted for all of the glucose utilized at both temperatures, indicating that the production of ATP by L. lactis or L. bulgaricus at 40 °C was not coupled closely to the utilization of ATP in the synthesis of bacterial mass.