Glycinin is one of the dominant storage proteins of soybean seeds. Previous studies showed that modified proglycinins, the variable regions of which were inserted with oligopeptides composed of four continuous methionines, could be synthesized in Escherichia coli and exhibited better food functional properties than the native glycinin (C.-S. Kim, S. Kamiya, T. Sato, S. Utsumi and M. Kito, Protein Engineering 3 (1990) 725–731). To investigate whether the modified glycinins would accumulate in plant tissues, the normal and modified cDNAs were placed under the control of the cauliflower mosaic virus 35S promoter in the binary vector pBI121, and then inserted into the genome of tobacco by Agrobacterium-mediated transformation. Both normal and modified glycinins accumulated in the leaves, stems and seeds, and no differences in the level of accumulation were observed among the expressed proteins in the leaves and seeds. The normal and modified glycinins expressed in each tissue were present as the correct-size proteins. The proteins expressed in each tissue were processed to the mature form, and those expressed in the seeds assembled into hexamers. These results support the possibility that we can create novel soybean plants which can produce modified glycinins having better nutritional and functional properties.