DNA hybridization with the insecticidal crystal protein gene cryIIA (formerly cryBI) of Bacillus thuringiensis supspecies kurstaki has shown that subspecies kurstaki contains a cryIIA-related sequence in addition to the cryIIA gene (Donovan et al., 1988a). We have cloned the cryIIA-related sequence and have determined that the sequence, which has been designated cryIIB, is 89% identical to the cryIIA gene. Recombinant B. thuringiensis cells harbouring the cloned cryIIB gene produced very little CryIIB protein. A high level of production of the CryIIB protein was achieved by fusing the regulatory region of the cryIIIA crystal protein gene to the cryIIB gene. The CryIIB protein was found to be highly toxic to Lymantria dispar, Heliothis virescens and Trichoplusia ni, and was not toxic to Aedes aegypti.