A study was performed on the antiviral effects of human interferon-beta (IFN-beta, MR-21) produced by a normal human diploid fibroblast cell strain. Of 4 DNA and 9 RNA viruses used in this study, all were inhibited by the IFN-beta and the IC90S obtained were approximately 10(1)-10(3) IU/ml. Results showed that IFN-beta had a very wide antiviral spectrum. The IFN-beta was able to induce 2',5'-oligo A synthetase activity in RSa, HeLa S3 and M08 cell lines but not in HEC-1C cell line lacking receptors for IFN-beta. This strongly suggests that one of the antiviral mechanisms might function through the induction of 2',5'-oligo A synthetase activity through the IFN-beta receptor.