We have transformed different pea genotypes, some which exhibit nodulation-defective or supernodulation phenotypes, with two distinct Agrobacterium strains to examine their endogenous hormone balance. Varying responses to A. tumefaciens or A. rhizogenes revealed pea genotypes that had unusual hormone levels or sensitivity to phytohormones. This was confirmed by HPLC and ELISA analysis as well as by investigating the effects of exogenous auxin and cytokinin on the transformation responses of the different genotypes. The differences among the genotypes in forming either roots or tumors upon infection with Agrobacterium enabled us to carry out a genetic analysis of these traits. We found that the capacity for root formation was inherited as a monogenic, dominant trait whereas the ability to form tumors was polygenic. These results suggest that these genes may be important for the regulation of endogenous phytohormone levels.