ASPARTIC DECARBOXYLASE OF NOCARDIA GLOBERULA 225 transamination mechanism. However, if a transamination reaction is taking place it is apparently concerned with some amino acid other than glutamic acid. SUMMARY 1. Acetone-dried powders of a strain of Nocardia globerula possess aspartic decarboxylase activity but are inactive towards all other amino acids tested. 2. The enzyme can be used for the quantitative estimation of L-aspartic acid in protein hydrolysates and is stable for long periods. I am indebted to the Medical Research Council for a Scholarship for Training in Research Methods. My thanks are also due to Dr S. V. Perry for a gift of [15N]aspartic acid, to Mr B. E. Boon for the operation of the mass spectrometer and to Mr M. W. Rees for a gift of edestin.