Antigen CD5 is the glycoprotein which belong to the scavenger receptor cysteine-rich family. Mainly there is on the T cells subpopulation. During fetal life B CD5+ cells are major subpopulation of B cells in the spleen, lymph nodes and there are also in the cord blood. In adult CD5+ cells are minor subpopulation (27%) of B cells from the peripheral blood. CD5 there are on chronic lymphocyte leukaemia B cells (B-CLL) also. Usually expression CD5 on B-CLL cells associated with weak or lack expression of the surface immunoglobulins and CD79 beta, CD20, CD22, CD21 (CR-2), CD35 (CR-1) antigens. It appeared interesting to compare the expression of CD5 antigen (the mean fluorescence intensity--MFI of CD5) on B cells from the cord blood, adults peripheral blood and B-CLL patients. MFI of CD5 on B and T cells were also compared in each groups. MFI of CD 19 was studied too. Lymphocytes from the cord blood (11 assays), adult peripheral blood of healthy volunteers (18 assays) and the peripheral blood of no treated patients with B-CLL (56 assays) were studied. The immunological phenotype of lymphocytes was evaluated with the monoclonal antibodies anti-CD5 and anti-CD19 by the flow cytometry method. We have demonstrated that MFI of CD5 on B cells from patients with B-CLL was strongest and weakest from normal individuals. MFI of CD5 on T cells from patients with B-CLL is stronger in comparison to healthy volunteers. MFI of CD19 is weakest on cells from patients with B-CLL and strongest in normal individuals. On the basis of the our results and other medical papers we suggest on the one hand that biology of B-CLL depend on deficit antigens specific for B cells lines on the other hand depend on overexpression of CD5 antigens on leukaemic B and T cells also.