Bacillus thuringiensis toxin (BT) is one of the best known insecticidal toxins which are synthesized during sporulation of cells. Various strains of Bacillus thuringiensis produce various forms of crystalline inclusion body and show different spectrums of insecticidal activities. B. thringaiensis subsp. $quot;israelensis$quot; encodes Diptera-specific BT and are toxic to the larvae of mosquitoes and black flies. To identify toxin genes of B. t. $quot;israelensis$quot; CNA412, gene-specific oligonucleotide probes to N-terminal and C-terminal of the gene encoding 66 kDa crystal protein were synthesized and utilized as probes for screening. Southern blot analysis showed they hybridized to about 9 kb DNA fragment. Structure of the gene was identified by restiction enzyme mapping and nucleotide sequencing.