The effect of ethylene on the uptake, distribution and polar transport of C(14) from indole-3-acetic acid-2-C(14) and naphthalene acetic acid-1-C(14) in tissue sections was studied. Test species were cotton (Gossypium hirsutum, L.) and cowpea (Vigna sinensis, Endl.). Generally, incubation of tissue or intact plants with ethylene reduced the degree of polar auxin transport. Ethylene inhibited the movement of both auxins in stem tissue and IAA in petiole tissue of cotton. The effect of ethylene on auxin movement in cow-peas was more complex. Ethylene apparently inhibited transport in younger petiole and stem tissue, but stimulated the process to a small but significant degree in basal petiole segments.Ethylene, in some experiments, reduced C(14) (auxin) uptake. This reduction was consistently smaller than the inhibition of transport. Effects upon transport were observed when uptake was not different. Differences in uptake declined as the period of incubation with auxin was lengthened, but transport was inhibited for up to 23 hours.It is proposed that ethylene may, through its effect on transport, cause localized shortages and surpluses of auxin which in turn contribute to symptoms now associated with the response of sensitive species to ethylene.