Bacillus thuringiensis (Bt) cyt genes coding hemolytic and cytolytic toxins constitute a gene family, which are divided into two groups: cyt1 and cyt2. A novel cyt2 gene was detected from a soil-isolated Bt strain T301, which was highly homologous to cyt2Ba1 and finally designated cyt2Ba7. Until now, Cyt2Ba has not been expressed alone in Bt or other hosts. In this study, the cyt2Ba7 gene was cloned into the vector pQE30 and expressed as a fusion protein with 6 x Histidine residues in Escherichia coli. Unlike cyt] A, cyt2Ba7 was freely expressed and formed cytoplasmic inclusions without the need for a "helper" protein. The 6 x His-tagged Cyt2Ba7 was purified in one step by Ni-NTA affinity chromatography, examined cytolytic activity on Sf9 cells, and developed as an antigen to obtain the antiserum against Cyt2Ba by subcutaneous injection into rabbits. This gene was also cloned into the Bt-E. coli shuttle vector pHT3101 and expressed in Bt strain 4Q7. Immunoblotting analysis revealed that the antiserum was remarkably selective and specific to Cyt2Ba.