The effect of 5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid (acifluorfen) on the translocation of the14C-labeled auxins 2,4,5-trichlorophenoxyacetic acid (2,4,5-T-1-14C) and indole-3-acetic acid (IAA-1-14C) was determined. The auxins and acifluorfen were injected into the stem at the cotyledonary node of 9-day-old bean (Phaseolus vulgaris L. cv Tenderpod) seedlings. The plants were harvested 4 h after treatment and analyses of14C were made of various plant parts. Acifluorfen increased 2,4,5-T,-1-14C translocation out of the treated area and especially into the large primary leaves. This translocation pattern is indicative of apoplastic translocation and suggests that acifluorfen inhibited vein loading of the auxins. Acifluorfen affected auxin translocation in the dark as effectively as in the light even though the herbicidal effects of acifluorfen are known to be expressed only after light treatment.