DeltaFosB is a truncated form of a FosB transcription factor, which is created by alternative splicing. Previous work has shown that transgenic mice expressing DeltaFosB both in the retina and in the lens developed a posterior subcapsular cataract resulting from the misalignment of the fibres in the suture region. In the previous study, it was not clear whether DeltaFosB expression was required in both tissues to produce the cataract. Therefore, DeltaFosB expression targeted to either the lens or the retina was undertaken in order to clarify the contribution of each tissue to cataract development. For lens expression, the R2betaB1DeltaFosB construct was synthesized (R2, an enhancer; betaB1, a chicken betaB1 crystallin gene promoter fragment). For the retina, RhoDeltaFosB was prepared. As a promoter, the bovine rhodopsin upstream region was used. DeltaFosB expression in heterozygote animals was monitored by Western blotting. Cataract development in heterozygotes of R2betaB1DeltaFosB transgenics and in both heterozygotes and homozygotes of RhoDeltaFosB transgenics was followed by slitlamp examination. The transgenic mice prepared with RhoDeltaFosB expressed DeltaFosB only in the retina and showed no sign of lens opacity. One line of the R2betaB1DeltaFosB transgenic was found to have expression only in the lens and developed posterior subcapsular cataract. We concluded that retinal expression of DeltaFosB is not sufficient to cause cataract while expression exclusively in the lens produces posterior subcapsular cataract.