Indol-3yl-acetic acid (IAA) applied to sterns of Phaseolus vulgaris seedlings, decapitated above primary leaves, enhanced the mobilization of 14C-metabolites to the treated stumps and this effect was apparent within 3–6 h of applying the hormone. More than 90 per cent of the total 14C-activity transported to the stumps was detected in the alcohol-soluble extracts. In all treatments, less than 5 per cent of the 14C-photosynthate exported from the primary leaves was translocated upwards. Accumulation of 14C-activity was also increased when the IAA was applied laterally to intact internodes. This effect was obtained when 14C was supplied either above or below the point of hormone application. By selective heat girdling, it was shown that the auxin affected 14C transport when either the root ‘sink’ was removed or transpiratory flow of water through the treated internode was maintained. Decapitated stems treated with plain lanolin for 3 d were found to retain their responsiveness to auxin in terms of enhanced metabolite transport. Heat-girdling experiments and estimates of 14C transport velocity suggested that most of the 14C movement was restricted to the phloem of treated stumps. Similar effects of IAA on a transport in excised stem segments of Phaseolus vulgaris were observed.