Crown gall tumors produced octopine or nopaline or neither compound, depending on the bacterial strain that incited the tumor. The genes specifying production of octopine or nopaline by the tumor were transferred to recipient bacterial strains when the large plasmid associated with virulence was transferred by either conjugation or deoxyribonucleic acid-mediated transformation. Our results, which confirm the work of others (Bomhoff et al., 1976; Goldman et al., 1968; Petit et al., 1970), indicate that, in general, the strains that utilize octopine induce tumors that synthesize octopine, and those that utilize nopaline induce tumors that synthesize nopaline. However, there were several notable exceptions. One class utilized both octopine and nopaline, but the tumors induced by these strains produced only nopaline. Another class utilized nopaline, but their tumors synthesized neither nopaline nor octopine. Mutants were isolated from a number of either octopine- or nopaline-utilizing strains that no longer could utilize the relevant guanido amino acid. These strains, which were mutant in the gene specifying octopine or nopaline oxidase, still retained the permease for these amino acids as well as virulence. Tumors induced by these mutants still synthesized approximately the same levels of octopine and nopaline as tumors induced by their parents. These results suggest that the plasmid gene that determines production of octopine or nopaline by the tumor is distinct from the plasmid gene that determines their catabolism by the bacteria.