Glutamic acid and glutamine were determined separately by the decarboxylase method in 24 different animal tissues (including fetal material), and in 54 specimens of human blood plasma. The sum of the concns. of glutamic acid and glutamine was highest in brain cortex, heart, spleen and thymus (avg. 10-15 x 10-6 mol./g.). Avg. values below 5 x 10-6 mol./g. were found in ovary, thyroid and lung, and below 1 x 10-6 mol./g. in most other tissues. In the mammalian heart and in blood plasma, glutamine was present in greater quantities than glutamic acid. In other tissues glutamic acid predominated as a rule.