A strategy for the production of human interferon-α (IFN-α) subtype-specific antibodies, based on immunizing rabbits with short unique synthetic peptides coupled to protein carriers, has been validated. These peptides correspond to amino acid residues 99-111 of IFN-α 1, 50-57 and 103-116 of IFN-α2, and 37-50 of IFN-α4. The antipeptide antibodies anti-IFNα 1(99-111), anti-IFNα2(50-57C), anti-IFNα2(103-116and anti-IFNα4(C37-50) were tested by ELISA and Western blotting for their reactivity with immunoaffinitypurified recombinant human IFN-α 1, -α2b and -α4a. The anti-IFNα 1(99-111) and anti-IFNα 2(50-57C) reacted with their corresponding IFN-α and did not crossreact with the other IFN subtypes. The anti-IFNα 2(103-116) reacted with IFN-α 2b and also crossreacted slightly with the other subtypes. The anti-IFNα 4(C37-50) reacted well with IFN-α 4a, crossreacted with significantly lower affinity with IFN-α 1 and did not bind IFN-α2b. Residues 104-107 and 108-111 are the major components of the epitopes recognized by anti-IFNα 1(99-111) and anti-IFNα2(103-116), respectively, as determined by ELISA against overlapping octapeptides.