The effects of growth temperature on the aerobic growth yield with respect to oxygen consumption (Y0-grams [dry weight] per gram-atom of O) and the rate of maintenance respiration (m0-milligram-atoms of O/gram [dry weight] per hour) are reported for Escherichia coli B cultivated continuously in the presence of oxygen with limiting glucose. During anaerobic continuous culture, YATP(max) (grams [dry weight] per mole of ATP corrected for maintenance) increases from 10.3 to 12.7 as the growth temperature is lowered from 37 to 25 C. Over this same range, Y0(max) (Y0 corrected for maintenance respiration) rises from 12.5 to 28.8 and remains at the higher value down to 17.5 C. From 37 to 32 C, m0 increases from 0.9 to 4.4 but then falls to 1.5 as the temperature is lowered to 17.5 C. The value of m0 sharply rises some 13-fold as the temperature is raised to 42 C without a significant change in the value of Y0(max). Changes of Y0(max) are consistent with a temperature-sensitive doubling of the efficiency of oxidative phosphorylation, but the reasons for the changes of the rate of maintenance respiration are not known.