One neutralization unit is the amount of antiserum required to neutralize one unit of human interferon alpha (Hu-IFN-alpha ) to a 50% endpoint. Interferon was titrated with the use of the cytopathic effect inhibition assay as described [Rubinstein, S., Familletti, P.C., and Pestka, S. (1981) “Convenient Assay for Interferons,” J. Virol. 37, 755-758; Familletti, P.C., Rubinstein, S., and Pestka, S. (1981) “A Convenient and Rapid Cytopathic Effect Inhibition Assay for Interferon,” in Methods in Enzymology, Vol. 78 (S. Pestka, ed.), Academic Press, New York, 387-394]. In this antiviral assay for interferon about 1 unit/ml of interferon is the quantity necessary to produce a cytopathic effect of 50%. The units are determined with respect to the international reference standard for Hu-IFN-alpha provided by the National Institutes of Health [see Pestka, S. (1986) “Interferon Standards and General Abbreviations,” in Methods in Enzymology (S. Pestka, ed.), Academic Press, New York, 119, 14-23]. This material is prepared specifically for effective neutralization of Hu-IFN-alpha.