The essential characteristics of the primary and secondary pathways of carbohydrate catabolism in a radiation-resistant micrococcus were studied by means of the radiorespirometric tracer method. Measurements of relative rates and total percentage of C14O2produced from different carbon atoms of specifically labelled acetate, pyruvate, glucose, and gluconate, together with determination of the C14incorporation into cells, indicated that glucose was utilized mainly by the Embden–Meyerhof–Parnas glycolytic pathway in conjunction with the tricarboxylic acid cycle.Approximately 14 per cent of the glucose appeared to be catabolized via phosphogluconate decarboxylation.