It was established that high level of BCL-2 antigen inhibited suicidal cell death and prevented apoptosis induced by antitumor drugs. Due to the fact that evaluation of BCL-2 expression in bone marrow and peripheral blood cells could be an important prognostic factor in patients with malignant hematopoietic diseases, we decided to study the number of BCL-2+ nuclear cells and assess this antigen expression in the cells. Using monoclonal FITC-conjugated antibody, antigen BCL-2 was found in peripheral blood cells in children with both lymphoblastic (ALL) and non-lymphoblastic leukemia (NLL). At the same time the percentage of PCNA+ blood nuclear cells was investigated. The cells were analysed with a flow cytometer. The study carried out in a group of 12 ill and 7 healthy children showed significantly increased percentage of lymphocytes and neutrophiles PCNA+ and BCL-2+ in ALL, in comparison with a healthy control group. Exclusively an increased percentage of BCL-2+ lymphocytes and neutrophiles was observed in NLL patients. Due to a relatively small group of investigated patients we can not make a certain conclusion but preliminary analysis suggests a correlation between a high number of BCL-2+ cells and a long time without remission.