In order to verify the organs involved in determination of nodulation responses of soybeans carrying nodulation conditioning genes, Rj_2, Rj_3 and Rj_4, various genotypes of soybean plants, Rj_<2-4>, non-Rj and nitrate-tolerant symbiosis (nts) were separated into shoots and roots, grafted reciprocally and the effects of genotypes of scions on nodulation on the roots of various genotypes were examined. The following results were obtained. 1. The phenotypes of Rj genes, e.g. whether nodulation was effective or ineffective, were determined by the root genotypes. When the incompatible strains with genotypes of stock were inoculated, ineffective nodules were formed and their number did not influenced by the shoot genotypes. 2. When compatible strains with the genotypes of stock were inoculated, only effective nodules were formed. In these cases, the numbers of effective nodules did not influenced by Rj-genotypes of scions. However, when the scion of nts mutant was grafted on the stock of Rj-genotype, and compatible rhizobial strain with the genotypes of stock was inoculated, the phenotype was super-abundant nodulation.