FROM limited experimental evidence it has been assumed that kinins are relatively immobile in plants1. When the synthetic kinin, kinetin, is applied to the surface of a leaf its effects in retarding senescence or acting as a locus for the accumulation of metabolites are restricted to the treated parts2. A direct investigation of the movement of isotopically labelled benzyladenine within petiole segments of Phaseolus vulgaris now reveals that this kinin is not only transported readily through the tissues, but that the movement is also basipetally polar. Furthermore, the total amount transported is enhanced by the addition of indolyl-3-acetic acid (IAA).