1. The activity to synthesize aspartic acid from fumaric acid and ammonia and the activity to synthesize glutamic acid from citric acid and ammonia were examined with the cell-free extracts obtained from several strains of M. glutamicus and their mutants grown on glucose bouillon media. All of them were found to possess a strong activity of the latter but practically no activity of the former.2. The activities of aspartase, glutamic dehydrogenase, alanine dehydrogenase, leucine dehyrogenase, glutamic-aspartic transaminase, and glutamic-alanine transaminase were examined with the cell-free extracts obtained from the cells of M. glutamicus (parent strain) grown on different levels of biotin. Only glutamic dehydrogenase and transaminases were detected in ample amounts. No significant difference was found in the activities of enzymes involved in the ammonia uptake in the extracts of the cells grown on the different levels of biotin. 3. From the results 1 and 2, it is concluded that in M. glutamicus the principal mechanism of ammonia uptake is effected by TPN-linked glutamic dehydrogenase irrespective of the biotin level in the growth medium, and consequently, the biosynthesis of the amino acids belonging to glutamic acid family and aspartic acid family proceeds directly or indirectly via the synthesis of glutamic acid.