Bean leaf tumors induced by Agrobacterium tumefaciens strain 181 show enhanced growth in response to octopine or lysopine only if one of these compounds is present during the period of tumor induction. Either compound applied during this period results in tumors which subsequently respond to both. The combined action of the bacterium plus octopine or lysopine at induction is proposed to induce transcription of plant genes coding for enzymes involved in the degradation and/or biosynthesis of octopine and lysopine.