Antiviral preparation derived from fermentation broth of Penicillium stoloniferum. Originally described as a mixture of polysaccharides, the antiviral activity was subsequently attributed to the induction of interferon by a double-stranded RNA virus in the fungus. Produced by submerged culture fermentation, using P. stoloniferum var. ATCC 14586: W. M. Stark et al., US 3108047 (1963 to Lilly). Induction of interferon production: W. J. Kleinschmidt et al., Proc. Natl. Acad. Sci. USA 52, 741 (1964). Identification of P. stoloniferum virus: L. F. Ellis, W. J. Kleinschmidt, Nature 215, 649 (1967); W. J. Kleinschmidt et al., ibid. 220, 167 (1968).