The pathogenesis of B-cell chronic lymphocytic leukemia (B-CLL) has been linked to an overexpression of the chemokine receptor CXCR4 and increased in vitro functional response to its natural ligand CXCL12 (SDF-1). The CXCR4/SDF-1 system appears to be important for tissue localization and increased survival of B-CLL cells. The aim of our study was to examine if CXCR4 expression and SDF-1 blood levels were correlated to clinical and pathological stage of B-CLL. Flow cytometry and enzyme-linked immunosorbent assay (ELISA) techniques were used to determine CXCR4 expression and SDF-1 plasma levels, respectively, in a cohort of 51 patients diagnosed with B-CLL to correlate these measurements with several parameters that define the clinical stage of the disease. We confirmed that CXCR4 was consistently expressed on circulating B-CLL cells with a fluorescence intensity that was five-fold greater than in cells from healthy volunteers. There was a correlation between CXCR4 expression and leukocyte count ( r: 0.55, p<0.01), and CD19(+)/CD5(+ )cells ( r: 0.63, p<0.01). Interestingly, the group of B-CLL patients showed lower SDF-1 plasma levels compared to the control group. However, there was no correlation between CXCR4 or SDF-1 expression and the clinical stage of disease or the pattern of bone marrow infiltration. The results obtained suggest that other factors, and not only alteration in the SDF-1/CXCR4 chemokine system, must account for marrow infiltration of neoplastic cells observed in B-CLL and that CXCR4 could be involved in other features that exhibit malignant B cells, such as increased survival, rather than in their homing or migration to the bone marrow.