By the same method as described in the 1st report permeability of human leakemia cells to dyes was studied using the same dyes as in report Ⅲ comparing to that of matured granulocytes of normal human blood, The myelogenous leukemic cells showed an increased permeability for basic dyes and a depressed permeability for acidic dyes, giving similar data as in the cases of normal bone marrow cells of rabbits (s. Ⅳ Report). ACTH acted as to increase the permeability of both basic and acidic dyes. Nitromin and Azan showed a depressing effect on both series of dyes, especially Azan showed a marked inhibitory effects for the invasion of dyes. Nitrogen musturd B acted as to depress slightly the permeability of acidic dyes, too, but it showed not any effect on the permeability of basic dyes. From these data it was concluded that leukemic cells have similar characteristics for the passive permeability as those of normal young cells in bone marrow. The antileukemic mechanisms of several drugs were discussed from the view point of permeability.