In the present study the gene expression of cytokines promoting in vitro myeloma-cell growth was investigated by Northern blot analysis using total RNA of 36 tumour samples of patients with multiple myeloma (MM) or plasma cell leukaemia and poly(A)+ RNA of 10 human myeloma cell lines (HMCL). These cytokines included interleukin (IL)-1 alpha, IL-1 beta, IL-3, IL-6, granulocyte-macrophage (GM)-colony-stimulating factor (CSF) and granulocyte (G)-CSF. IL-1 beta, IL-6 and G-CSF genes were coexpressed in most patients, although at variable levels. IL-1 alpha transcripts were detected in 32% of patients in whom coexpression of IL-1 beta gene was found. IL-3 gene was not expressed in patients' cells and GM-CSF mRNA was detected in only 1/32 patients. No detectable transcripts for the above cytokines were present in HMCL, whereas IL-6 gene was expressed in 2/10 HMCL. We also looked for the presence of transcripts for IL-2, leukaemia inhibitory factor (LIF) and transforming growth factor (TGF)beta in cells of tumour samples from the same patients and in HMCL. IL-2 gene was not expressed in MM patients and HMCL. Weak expression of LIF gene was detected in three patients (9%), and transforming growth factor beta (TGF beta) mRNA was observed in 12/12 tumour samples analysed and all HMCL. These results suggest that, among cytokines shown to control myeloma-cell growth in vitro, IL-1, IL-6 and G-CSF could play a role in the development of myeloma disease in vivo.