Imazamox is an imidazolinone herbicide used to control many grasses and broadleaf weeds in leguminous crops such as soybean, alfalfa, and dry bean; however, imazamox cannot be used on red lentil due to unacceptable injury. Studies were conducted to compare imazamox absorption, translocation, and metabolism in red lentil and dry bean to determine if any or all of these factors contributed to differential crop sensitivity. Radiolabeled imazamox was applied to three young red lentil leaves and the youngest, fully expanded dry bean trifoliolate leaf. Absorption, translocation, and metabolism were followed over a 96-h time course. Red lentil had more rapid absorption compared to dry beans with 64 and 54% of the applied dose absorbed 12 h after treatment (HAT), respectively. Maximum absorption was also greater in red lentil than dry bean, 79 and 61%, respectively. Translocation out of the treated leaf was significantly higher in red lentil compared with dry bean, 16 and 0.5%, respectively, at 96 HAT. Translocation was greater to red lentil roots compared to shoots, 9 and 7%, respectively, at 96 HAT. In dry bean only 14% of applied 14C-imazamox remained intact 24 HAT, while 79% of the radioactivity was imazamox in red lentil 24 HAT. Both species metabolized the herbicide to more polar metabolites. The inherent sensitivity of aceolactate synthase (ALS) from dry bean and red lentil was also evaluated. ALS from both species had similar I50 values for imazamox, 7.2 and 8.2 µM, respectively. The combined effects of increased imazamox absorption and reduced imazamox metabolism are the major contributors to differential selectivity between dry bean and red lentil. Rapid imazamox metabolism in dry bean significantly limited herbicide translocation out of the treated leaf.