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Purpose Bruton’s tyrosine kinase is crucial for B-lymphocyte development. By the use of gene expression profiling, we have identified four expressed sequence tags among 38 potential Btk target genes, which have now been characterised. Methods Bioinformatics tools including data mining of additional unpublished gene expression profiles, sequence verification of PCR products and qualitative RT-PCR were used. Stimulations targeting the B-cell receptor and the protein kinase C were used to activate whole B-cell splenocytes. Results Target genes were characterised as Lim domain only 7 ( Lmo7 ); Myosin1e ( Myo1e ); SAM and SH3 domain containing 1 ( Sash1 ); and Mucolipin2 ( Mcoln2 ). Expression was found in cell lines of different origin and developmental stages as well as in whole B-cell splenocytes and Transitional type 1 (T1) splenic B-cells from wild type and Btk-defective mice, respectively. By the use of semi-quantitative RT-PCR we found Sash1 not to be expressed in the investigated haematopoietic cell lines, while transcripts were found in whole splenic B-cells from both wild type and Btk-defective mice, whereas Lmo7 , Myo1e , and Mcoln2 were expressed in both B-cell lines and primary B-lymphocytes. Except for Lmo7 , the transcript level was similarly affected by stimulation in control and Btk-defective cells.