The course is analyzed of myeloblastic leukemia in twelve participants in the elimination of the aftermath of the Chernobyl Atomic Power Plant breakdown. The iliac trepanobiopsies bone-marrow hemopoiesis is studied. A gross depression of normal hemopoiesis has been revealed together with a fibrous transformation of the bone marrow, which fact suggests a profound damage to the hemopoietic micro-surroundings, being a cause of ineffective hemopoiesis, of grave course of the illness, and of failure to respond to cytostatic therapy.