Using the hybridoma technique, a series of secretingmonoclonal antibodies (McAbs) against recombinant human interleukin-6 (rhIL-6) have been established after immunization of Balb/c mice with rhIL-6. Three of these McAbs 2H₂, 1D₂ and 4B₄ were well characterized. Their Ig class and subclass were determined as IgG1 and IgG2a respectively. These McAbs reacted with a high degree of specificity to rhIL-6 and did not have cross-reactivity with many other cytokines and irrelevant proteins. Immunoblotting results showed that these McAb only recognized a single band of rhIL-6 with molecular mass of 21 ku. These McAb reacted strongly with IL-6 molecules with an affinity constant (K_aff) 1.62×10⁹ (mol/L)^-1.