SUMMARY: Extracts of 288 plants, mostly British, were examined for suppressive action on the development of a bacteriophage of Pseudomonas pyocyanea. Many possessed this property and eight of them suppressed the growth of phage at concentrations less than one-tenth of those which affected the growth of the host, Ps. pyocyanea.Extracts from 142 of the plants were tested against Influenza A virus in embryonated eggs and twelve of them suppressed virus multiplication. All extracts active against Influenza A virus were also active against the bacteriophage. Four extracts tested against Influenza A in mice were inactive. Eight extracts were investigated further; these were inactivated by proteins and were only active when in direct contact with the virus in protein-free media, Activity was closely associated with the tannin content of the extracts and could not be separated from it. Commercial tannins were also highly active in protein-free media. At some stages of our work the identification of the samples was unable to keep up with the rate of supply, and although a portion of the plants was always kept for examination it was not always possible to decide upon the specific name. Difficulty also arose when an extract from a florist's variety was under test. In both these cases the generic name followed by (?sp.) appears in Table 7. In some cases several varieties of the same species were tested. METHODS Preparation of extractsPlants in as fresh a condition as possible were macerated in distilled water plus 15 yo (v/v) industrial spirit, using a bench macerator with high-speed

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