The antibody reacts with natural and recombinant mouse interleukin 6 (IL-6) as assessed by ELISA. The antibody inhibits the biological activity of natural and recombinant mouse IL-6 as determined with the B9 cell bio-assay. The antibody cross-reacts with natural rat IL-6. IL-6 is a pluripotent 20-22 kDa cytokine which plays a role in the pathophysiology of severe infection and regulates the immune response, acute phase reaction and hematopoiesis. IL-6 plays a critical role in B-cell differentiation to plasma cells and is a potent growth factor for plasmacytoma and myeloma. Continuous IL-6 gene expression makes an essential contribution to a multistep oncogenesis of plasma cell neoplasia. IL-6 is a very useful culture supplement for the generation of a high number of antibody-producing hybridomas.