Chemokines are a family of 8-10 kDa proteins with a wide range of biological activities including the regulation of leukocyte trafficking, modulation of haemopoietic cell proliferation and adhesion to extracellular matrix molecules. Using a panel of chemokine receptor-specific monoclonal antibodies (MoAb) in a multicolour flow cytometry approach we analysed the expression of the lymphocyte-associated chemokine receptors CXCR4, CXCR5, CCR5 and CCR6 in B cell acute lymphoblastic leukaemia (precursor B-ALL; six cases), B cell chronic lymphocytic leukaemia (B-CLL; 31 cases), multiple myeloma (10 cases), mantle cell lymphoma (MCL, four cases), follicular lymphoma (FL, three cases) and hairy cell leukaemia (HCL, five cases). We demonstrate that CXCR4, CXCR5 and CCR6 are differentially expressed in these B lymphoproliferative disorders depending on the maturational stage of the malignant B cell population investigated. In particular, we found that CXCR4 is strongly expressed on immature ALL blasts whereas no surface immunoreactivity for CXCR5, CCR5 and CCR6 was observed. By contrast, non-Hodgkin's lymphomas (NHLs) corresponding to more mature peripheral B cell subsets (ie B-CLL and MCL) exhibited high expression levels of CXCR4 and CXCR5. Analysis of terminally differentiated myeloma cells revealed a down-regulation of CXCR4, CXCR5 and CCR6. CCR5, which is not expressed in normal B cells, was also absent from the majority of NHLs. However, CCR5 staining was seen in three of five cases of HCL, representing the first example of cross-lineage aberrant chemokine receptor expression in malignant haemopoietic cells.