BACKGROUND For examination of surface characteristics of lymphocytes automatic analyzers of flow cytometry are used which make it possible to assess labelling with 2-3 monoclonal antibodies on one examined cell and provide thus more accurate data on the immunophenotype of proliferating cells. The objective of the present work was-using the method of flow cytometry and monoclonal antibodies-to detect surface signs on lymphocytes in the peripheral blood stream of patients with lymphatic leukaemia. RESULTS In 29 patients with chronic lymphatic leukaemia type B (B-CLL) CD signs were examined, using flow cytometry and the findings were compared with those obtained in a control group of 63 healthy subjects. Evidence of CD 19+ CD5+ lymphocytes (B1 cells) in B-CLL (83.4 +/- 15% vs. 3.5 +/- 1.9% in controls) was of diagnostic importance. These CD5+ B cells are polyreactive, "memory B" lymphocytes which contrary to "conventional" lymphocytes B2 (CD5-B) do not differentiate further to plasma cells. Accumulation of B1 (CD5+ B) lymphocytes was, on the other hand, associated in patients with B-CLL with a decrease of B2 (CD5-B) lymphocytes (2.8 +/- 4.0% vs 9.0 +/- 4.2%) (p < 0.01). This finding can in case of excess of B1 (CD5+ B) lymphocytes explain the tendency of patients with B-CLL to develop autoimmune complications (e.g. AIHA); and conversely a decrease of B2 (CD5-B) lymphocytes can lead to hypogammaglobulinaemia which is also associated with B-CLL. A tendency towards autoimmunity may be also promoted by a decline of so-called inductors of suppressor cells (CD 4+ CD45RA); in patients with B-CLL among CD4 T lymphocytes 32.5 +/- 15% CD 45RA+ cells were found, as compared to 43.0 +/- 14.8% in controls (p < 0.011) and a lower ratio of true suppressor T cells (CD8+ CD11b+) in patients with B-CLL: 47.0 +/- 17.6% CD11b+ from CD8+ cells, as compared with controls 80.4 +/- 13.3 CD11b from CD 8+ cells (p < 0.01). CONCLUSIONS The method of flow cytometry with double fluorescence thus contributes to the accurate diagnosis of B-CLL, to monitoring of the therapeutic effect but also to knowledge of the immunopathology of the disease.