Cytokine expression of potentially active B-cell growth factors (IL-2, IL-4, IL-6) was investigated by means of mRNA-expression in 29 cases of malignant non-Hodgkin B-cell lymphomas. Strong signals were found for IL-4 and IL-6 in two and five cases, respectively, whereas the majority of the remaining cases did not show any detectable mRNA-signals for these growth factors. Comparing these results with those of the immunohistochemistry, it could be demonstrated that at least in some of these cases the signal was due to an autocrine or paracrine phenomenon of the tumour cells.