AbstractNineteen methanolic crude plant extracts of Labiatae family, collected in Greece from different locations, were evaluated for cytotoxic activity against brine shrimps and three human cancer cell lines along with a normal mouse cells as a control cell line. In the brine shrimp lethality test, Mentha pulegium was the only sample found to be active with an LC50 value 347.3 µg/ml, while all remaining samples had LC50 values greater than 1000 µg/ml. In case of Caco‐2 and HepG2 cell lines, only one sample, namely Thymus parnassicus Halacsy, was active with LC50 values 44.6 and 50.3 µg/ml respectively, while against MCF‐7 cell line, two samples, namely, Clinopodium vulgare L. (LC50: 60.4 µg/ml), and Thymus parnassicus Halacsy (LC50: 54.7 µg/ml), were found active. Copyright © 2003 John Wiley & Sons, Ltd.