RECENT work by Gmelin and Virtanen1, concerning the isolation and elucidation of the structure of glucobrassicin, and its reaction with ascorbic acid in the presence of myrosinase to give rise to ascorbigen, prompted us to investigate some biochemical interrelations of indole derivatives in Brassica oleracea L. by means of labelled (radioactive) compounds. The main question in this connexion was why, in our previous communication2, we were not able to prove the presence of glucobrassicin in our material. According to Gmelin3, our method of working up the plant material was not suitable for demonstrating the presence of glucobrassicin in it. The reaction of glucobrassicin with ascorbic acid in the presence of enzymes (myrosinase) set free in the damaged plant tissue is so rapid as to make impossible the proof of the presence of glucobrassicin in the fresh juice.