Two peptides from the amino terminus of human interferon-beta were synthesized corresponding to amino acids 1-21 and 18-45. The peptides were conjugated to bovine serum albumin, and rabbits were immunized with either the (1-21)- or the (18-45)-peptide conjugate. Antibodies to the synthetic peptides were detected in the sera using a radioimmunoassay with 125I-labeled peptide. Two of the antisera, one against peptide 1-21 and one against peptide 18-45, immunoprecipitated [35S]interferon-beta. The former was used to study the biosynthesis of interferon-beta in human diploid fibroblasts. In cells induced with double-stranded RNA (poly(I:C] to synthesize interferon-beta, two intracellular proteins with estimated molecular weights of 23,000 and 18,000 were precipitated with the antiserum. Three exocellular proteins from the same induced cells were precipitated with molecular weights of 23,000, 18,000, and 10,000. Reduced amounts of the intra- and exocellular Mr = 23,000 component and enhanced amounts of the Mr = 18,000 component were observed when induced cells were treated with the glycosylation inhibitor tunicamycin. Neither the antibody to peptide 1-21, the antibody to peptide 18-45, nor a combination of both antibodies neutralized the interferon-beta antiviral activity. We conclude that the amino terminus of interferon-beta may not be involved in the binding of interferon-beta to its receptor.