22 mice with L-1210 leukemia treated with quinoline dibromide were studied histologically. Two ways of the development of leptomeningeal infiltrates in the brain are established. The first is due to the growth of uninhibited by treatment bone-marrow leukemic infiltrates (LI) of the skull, while the second-when the above infiltrates are suppressed-due to the proliferation of leukemic cells penetrating from the dura mater to the leptomeninges protected by the hematoencephalic barrier from the effect of anticancer drugs. when the recurrence of leukemia occurs the growth of bone-marrow LI continues resulting in the additional migration of leukemic cells to the leptomeninges. These ways of the leptomeninx LI formation should be taken into consideration in the leukemia treatment.