Seven supernodulation mutants of soybean (Glycine max) derived from the cultivar Bragg were investigated for shoot control of the supernodulation response. Reciprocal grafts showed that supernodulation in all lines tested was obtained only if the genotype of the shoot was homozygous for the mutant allele(s). In addition two lines of Korean origin (selected in the field for increased nitrate tolerance) were included in the grafting studies. Under our experimental conditions nitrate tolerance could not be demonstrated in the Korean cultivars. Grafts gave near-control levels of nodulation, suggesting that the genetic basis of nitrate tolerance and increased nodulation in the Korean lines is different from that seen in the induced mutants of Bragg. The data suggest that, contrary to earlier reports with pea (Pisum sativum) mutants, no root control of supernodulation could be demonstrated. Furthermore the results point to a possible novel regulatory system governing nodule numbers and patterning which involves an intertissue transfer of a chemical signal.