Cyanobacterium Synechocystis PCC6803 was used as a model system for a prolonged delivery of insecticidal crystal proteins of Bacillus thuringiensis subsp. israelensis in the water surface. The bt8 gene, encoding a 128 kDa (Bt8) mosquitocidal protein, and the 28kd gene, encoding a 28 kDa cytotoxic protein, were integrated into the cyanobacterial chromosome. The genes were expressed under the control of the psbA promoter, derived from the tobacco chloroplast genome. The Bt8 protein produced by the cyanobacterium was toxic to mosquito larvae. The 28kd gene expression in the cyanobacterium was very low, partly owing to the low level of steady state mRNA. With the same system, it was demonstrated that the herbicide-resistance gene bar could be used as a new selectable marker in cyanobacterial transformation experiments.