Fifty isolates of chitinase (Cts)-producing bacteria were collected from soil samples and tested for their ability to degrade chitin using colloidal chitin agar as the primary plating medium. The results indicated that three isolates could degrade chitin at high pH. Further studies also demonstrated that crude Cts preparations from Bacillus circulans (Bc) No. 4.1 could enhance the toxicity of Bacillus thuringiensis subsp. kurstaki (Bt-k) toward diamondback moth larvae. Thus, it might be useful to increase the toxicity of B. thuringiensis (Bt) toward target insects by introducing a Cts-encoding gene (cts) into Bt. To investigate the expression of cts in Bt, cloned cts from Aeromonas hydrophila (pHYA1) and Pseudomonas maltophilia (pHYB1, pHYB2 and pHYB3) were cloned into the shuttle vector pHY300PLK and transformed into Escherichia coli DH5 alpha using 4-methylumbelliferyl beta-D-N,N'-diacetylchitobioside (4-MUF GlcNAc) as the detecting substrate. The four plasmids were then introduced into B. thuringiensis subsp. israelensis (Bt-i) strain c4Q272 by electroporation. Various transformants harboring cloned cts were selected, and expression and stability of the plasmids in Bt were studied.