Antineoplastic activity against human gastric, colon and hepatocellular carcinoma cell lines were measured in 100 extracts from 80 medicinal plants using MTT (3-[4, 5-dimethyl thiazol-2-yl]-2, 5-diphenyl tetrazolium bromide) method. Seventeen extracts from fourteen plants, all of which have previously been reported to have antineoplastic effect, had $IC_{50}$(50% inhibitory concentration) values of less than $230{;}{mu}g/ml$ in at least one of the three cell lines. Extracts from remaining sixty-six medicinal plants failed to show significant cytotoxic effect at the concentration of less than $230{;}{mu}g/ml$.