IN 1939, Kogl and Erxleben1 reported the isolation from tumour proteins of amino-acids of the d-series, chiefly d-glutamic acid, and developed a new theory of the origin of malignant tumours based on the view that malignant growth depends upon the alteration of the proteins in tumour cells owing to the inclusion of racemized amino-acids. Chibnall et al.2 failed to detect the unnatural form of glutamic acid in hydrolysates from tumour proteins. Graff3 was also unable to reproduce Kogl's results. Accord- ing to Kogl4, the failure of these authors to obtain d-glutamic acid was due to the fact that they used a different method for its isolation. White and White5 and Arnow6 confirmed the results of Kogl in a small number of experiments, but Dittmar7, who followed Kogl's technique for the isolation of glutamic acid, failed to detect the d-form of this acid in proteins from the growing parts of different types of sarcoma, though he was able to establish racemization of glutamic acid in the proteins from necrotic malignant tissue.