SUMMARYSpores of Bacillus thuringiensis contain a toxin active against lepidopterous larvae. This toxin can be solubilized by extraction with reagents which dissolve the protein crystal of B. thuringiensis. It is inactivated by crystal-specific antiserum. Spores of Bacillus cereus contain a similar toxin although the specific activity is much lower than the spores of B. thuringiensis. The B. cereus toxin contains a single major polypeptide component. Toxic activity can be solubilized from spores of both species by incubation with gut juices from Pieris brassicae.

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