Presented study analyzed the immunophenotypic characteristics and antigen density of peripheral blood (PB) and bone marrow (BM) cells of 23 patients with B-chronic lymphocytic leukemia (B-CLL) and 10 control subjects using flow cytometry. The patients were subclassified into two groups. Group I formed 13 patients with B-CLL at the time of diagnosis and group II 10 patients with B-CLL after the therapy but not in remission. For definition of B-CLL cells we used immunological marker analysis of surface markers characteristic for B-CLL pattern: CD5, CD19, CD20, CD23 and HLA DR and enumeration of fluorescence intensity of these markers given by molecular equivalent of soluble fluorochrome--MESF. In group II of B-CLL patients, who were already treated, in PB and BM somehow lower MESF values for CD19, CD20 and CD23 markers and higher MESF values for CD5 marker (in PB and BM) than in group I patients have been detected. The MESF level of HLA DR marker was little higher in group II than in group I B-CLL patients. However in PB and BM the percentage expression of HLA DR and CD19 markers in both patients groups was approximately the same. The values of HLA DR, CD19, CD20, CD23 and CD5 markers (% expression and MESF values) in both patients groups with B-CLL were significantly higher versus controls (p<0.001 resp. p<0.01) even in PB and BM. In conclusion, in our study we observed that the patients with B-CLL after therapy (group II) had similar or a little smaller (except CD5) but nonsignificantly decreased expression level of markers characteristic for B-CLL, but the MESF values of some of them (CD19, CD23) were significantly (p<0.05) decreased when compared with untreated B-CLL patients (group I). The determination of antigen density (MESF values) may be an important marker to characterize the leukemic cells. Our results showed that chemotherapy did not influence in a significant level the antigen modulation of B-CLL cells, however, could influence MESF values of some characteristic markers. Quantitative analysis of some markers in B-CLL cells seems to offer valuable information concerning possible influence of some chemotherapeutics on antigen equipment of leukemic cells.