The preparation of a panel of hybridoma cell lines secreting monoclonal antibodies (MAbs) specific for Recombinant Porcine Alpha I Interferon is reported. Of these MAbs, 28 were subcloned and 21 secreted their antibody during several months. They were partially characterized for their ability to bind and neutralize Alpha Interferons (IFNs-alpha) from different animal species. All the clones bound Recombinant Porcine IFN-alpha 1, 8 bound Human leukocyte IFN, and one bound recombinant Human IFN-alpha 2b, but not IFN-alpha 2a. Two screening procedures were used for the detection of specific MAbs: neutralization assay and immunosorbent binding bioassay. This last method appears to be simple and very sensitive since it permits to detect 100 pg/ml MAb. In addition it can detect weakly, as well as strongly neutralizing antibodies. Probable mechanisms involved in this assay, and possible applications of this method for IFNs-alpha subtyping are discussed.