We have investigated the influence of Sanicula europaea L. extracts on influenza virus growth in MDCK cells. Fractions I, II: and III separated from Sanicula extract with Sephadex column chromatography were found to be non-toxic against MDCK cells. The growth of influenza A/PR/8/34 was completely inhibited by these fractions, while that of influenza B/Lee/40 was not affected. Fractions II and III have been shown not to have a direct virucidal activity on influenza A/PR/8/34. Influenza A/Vic/1/75 produced microscopic plaques in the presence of the extract. In vitro RNA synthesis with viral RNA-dependent RNA polymerase was also inhibited by a water soluble extract of Sanicula. These observations suggest that the Sanicula extract contains an anti-influenza virus substance. (C) 1996 Academic Press. Inc.