According to the conclusion of the International Programme on the Health Effects of the Chernobyl Accident (IPHECA) Haematology Pilot Project (1991-1995), there was no increase in the incidence of malignant disease in hematopoietic and lymphoid tissues after the Chernobyl accident. Nevertheless, since studies of A-bomb survivors indicate that the peak in morbidity may occur more than 10 years after radiation exposure, long-term studies of hemoblastoses and myelodysplastic syndromes are needed today. Study of these leukemias and lymphomas that are potentially induced by ionizing radiation must include both fundamental and applied approaches, i.e., A) epidemiological design; B) utilization of modern methods of diagnosis (cytomorphology, immunocytochemistry, cytogenetics); C) studies of gene mutations, mechanisms of apoptosis, and G1 delay; D) monitoring of oncogene and multidrug resistance gene expression, and E) tracking changes in cell-cell signaling in the bone marrow microenvironment.