Absorption and translocation of aminocyclopyrachlor (AMCP) was investigated in black walnut. Radiolabeled AMCP was applied foliarly as a free acid, and basally as a free-acid-formulated oil-soluble liquid and as a methyl ester emusifiable concentrate. Maximum absorption was 68% for the methyl ester, 47% for the free-acid oil-soluble liquid, and 8% for the free acid when evaluated as percent applied. When recovered AMCP was presented as Bq g−1, no difference was observed in AMCP absorption or translocation of 14C-labeled material out of treated plant parts. Recovery of applied radiolabeled material in the roots from basal applications was 5 to 11% 72 h after treatment (HAT), compared with 0.8% recovery from a foliar application. Regardless of chemical form or formulation type, comparable injury was observed within 72 HAT despite low levels of translocation.