The antibody neutralizes mouse interleukin 6 (IL-6). It does not cross-react with LPS (the component of the bacterial cell wall which is considered responsible for the toxicity of gram-negative bacteria) and TNF-alpha nor does it bind to either human or rat IL-6. The antibody inhibits IL-6 induced proliferation of the B9 assay. 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 haematopoiesis. 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.