The inhibitory effect of Inula sesquiterpene lactones on the growth of Phaseolus vulgaris was tested and the abnormality of the stem organization caused by the lactones was also examined. The longitudinal growth of the young stem and the expansion of the young leaf were stopped by the application of the lactones. However, this inhibitory effect was appeared and strictly restricted within the treated area. So the young shoot was observed for possible bending as a result of the unilateral application of the lactones. When the application of the lactones into the medium, the growth of the plant was entirely repressed. However, the growth of shoot and re-initiation of root were started after the plant was transfered to the lactone free medium. And partial reversal of inhibition of the stem growth was achieved by the additions of gibberelline and the lactones.