The binary (51 and 42 kDa) and 100 kDa mosquito larvicidal toxins of Bacillus sphaericus are expressed at different growth stages of Bacillus. The genes encoding the binary toxin were expressed using T7 expression system of E. coli. In addition, a PCR amplified product containing the coding sequences of the 100 kDa toxin was cloned upstream to the binary toxin genes, and both the toxins were co-expressed in E. coli. Expression studies with these constructs in different E. coli hosts showed that when these two toxins were co-expressed, there was no augmentation of toxicity in comparison to the construct expressing the binary toxin alone. This result apparently indicates that there is no synergism between these two toxins.