The cell agar plate screening method for antitumor cell effect (Yamazaki et al., 1956) was applied to 1300 organic compounds. The method is based on the inhibition of the dehydrogenase activity (on 2, 6-dichlorophenol indophenol) of cancer cells mixed in the agar containing Hanks' solution. The inhibitory activity against dehydrogenase system of cancer cell is arbitrarily expressed by mm in diameter of non-reduced zone on the agar surface around the cylinder containing a drug suspension, in a way analogous to the cylinder plate assay for antibacterial substances. The preliminary report was already published (Mizuno et al., 1957) .

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