Supernodulating soybean mutant, SS2-2, was isolated through mutagenesis of Sinpaldalkong 2 with ethyl methanesulfonate (EMS). Recently, two independent studies were performed to characterize the regulation of supernodulation in the mutant. The first experiment was performed to evaluate the effect of NO₃ on the nodulation, nitrogenase activity, and growth of supernodulating soybean mutant and its wild type. Greenhouse study revealed that supernodulating soybean mutants, SS2-2 and nts 382, showed more nodules and nodule mass, and greater C₂H₂activity than the wild type, Sinpaldalkong 2, regardless of the level of exogeneous nitrogen supply. On the other hand, total dry weight of SS2-2 mutant, which was smaller than Sinpaldalkong 2, did not respond to the various NO₃-N level. From the reduced top growth and high nitrogen fixing ability of supernodulating mutants, it was surmised that supernodulating mutant could be a good biological material to protect agricultural environments from pollution through the reduction in nitrogen fertilization as well as to maintain fairly high yield by increasing planting density. In the second experiment, grafting study was performed to identify the origin of the factors regulating the nodulation in supernodulating soybean mutant SS2-2. Significant shoot genotypic effects were observed on nodule number, nodule dry weight, and C₂H₂ reduction activity per plant, whereas varying root genotypes had no effects, indicating that supernodulating characters are controlled by a graft-transmissible shoot factor. Genetic analysis for supernodulation characters are currently being studied at the DNA level to help locate the gene conferring supernodulation.