Summary.The experiments here reported on treatment of spontaneous leukemia in mice with nitrogenized mustard gas — erasin — confirm the clinical results of such therapy insofar as they show a specific inhibitory effect on the leukotic tissue.Recovery of the animals was not aimed at, and probably it would not have been obtained either. But, at any rate, a complete remission may be said to have been obtained in those cases where all the organs examined were found to be free from tumor tissue, while the white blood count was brought down to a normal level.Possibly another series of experiments in which smaller doses of the remedy would be given for a considerable length of time, aiming at the recovery of the animals, might have given some different results. For the possibility cannot be excluded altogether that the large subtoxic doses perhaps have an inhibitory effect on the regenerative capacity of the organ