In vitro sensitivity testing was performed for 21 kinds putative anticancer drugs selected from references and information. Cellular damage of P815 mastocytoma cells following exposure to water extracts of drugs was evaluated by colony formation assay. Highly effective drugs with more than 50% inhibition of colony formation were seven (Houttuyniae Herba, Sanguisorbae Radix, Nepetae Herba, Manitis Squama, Lonicerae Flos, Amomi Semen, Polyporus), though not more effective than BCNU. According to the results of $^3H-thymidine$ incorporation assay for determination of selective cytotoxicity, 3 of these drugs (Houttuyniae Herba, Polyporus, Manitis Squama) were found to be low cytotoxic to normal mouse lymphoid cells. These findings suggest that the above 3 drugs may be used for effective anticancer drugs in vivo.