The methanol, dichloromethane, petroleum ether, 90% methanol and 1-butanol fractions of 40 Malaysian medicinal plants belonging to 25 families were tested for brine shrimp lethality. Various parts and fractions of eight (20%) plants, viz. Annona muricata, Cerbera odollam. Calophyllum inophyllum, Entada phaseoloides, Pithecellobium jiringa, Crotolaria retusa, Morinda elliptica and Sellaginella willdenovii showed very strong toxicity $(LC_{50}:$<$100;ppm)$. The methanol extract of the seed of Calophyllum inophyllum showed exceptionally toxic activity $(LC_{50}:$<$5;ppm)$.