Six cases of leukemia were treated with an anti-leukemic substance, 6-mercaptopurine (“Mern”). In two cases of chronic myelogenous type and one case of chronic lymphatic type remarkable hematological and clinical improvement were observed. It was moderately effective in one case of subacute or acute myelogenous type but ineffective in one case of subacute or acute monocytic type. 6-mercaptopurine was practically as effective as the ordinal anti-leukemic substance. And there observed nothing of side effect especially on erythrocyte and thrombocyte, that is a remarkable good point of 6-mercaptopurine.
