Bc1-2 protein was analysed in cell cultures derived from non-Hodgkin lymphomas and chronic lymphocytic leukaemia patients. The presence of bc1-2 proto-oncogene protein product has been demonstrated on cytospin preparations utilising immunochemical methods. The correlation between the expression of the bc1-2 protein and the appearance of proliferation- or differentiation related figures was studied. The reported bc1-2 up regulation in malignant lymphoid cells was confirmed in haemo- and lymphopoietic progenitor cells as well as in TPA/PHA activated peripheral blood lymphocytes. In comparison to neoplastic cells lower intensity of bc1-2 positive staining in freshly isolated cells from non-leukaemic tissue was observed.