SUMMARYRespiration studies ofN. rubraconfirmed earlier qualitative studies on carbohydrate utilization. The inherent high endogenous respiration of the cells was reduced to less than 10% by shaking overnight in phosphate buffer (pH 7). The pattern of utilization varied with the age of the cultures used, e.g., 4-day old being metabolically more active than 7-day old on a number of the sugars.When one of the less readily utilized sugars was replaced in part by glucose, the oxygen uptake was considerably higher than with either sugar alone, showing that glucose stimulated the utilization of the other sugar. This effect was observed in mixtures containing 15–50% glucose.Although the oxygen uptake/mg dry weight varied considerably with different batches of cells of the same age, the same general trends were observed within an age group. This variation may be due to the random mixtures of cells of different ages in the seemingly uniform inoculum used initially. This was overcome by using as inocula frozen stock suspensions of 24-hour shake cultures ofN. rubragrown in a 0.07 M glucose medium.Such inocula were used in growth studies, in which the quantitative growth curves for several carbohydrates paralleled earlier growth studies. The patterns in mixtures of sugars confirmed the results from respiration studies.