The production of antiviral substances (I) from fetal or juvenile animal thymus is deep frozen immediately after slaughter and comprises: (i) grinding thymus in the deep-frozen state; (ii) exposing it to 5% peracetic acid vapor in vacuum for 4-8 hours; (iii) filtering with exclusion limit 30-100 kD; and (iv) purifying by column chromatography. (I) inhibit viral replication in infected human lymphocytes by a direct antiviral action or stimulate synthesis of the antiviral agents alpha , beta and psi -interferons by virus-infected lymphocytes.
