Ten corn inbred lines were field evaluated for their tolerance to DPX-M6316 at 32 and 64 g ai/ha. Inbreds ‘A619′, ‘A641′, and ‘ND246’ were highly susceptible to DPX-M6316; inbreds ‘A671′, ‘A632′, and ‘B73’ were highly tolerant; and inbreds ‘A654′, ‘CM105′, ‘W153R’, and ‘M017’ were intermediate in their response. The basis for differential tolerance was studied by comparing the susceptibility of acetolactate synthase (ALS) to inhibition by DPX-M6316 in tolerant A671 and susceptible A619, and by examining the absorption, translocation, and metabolism of DPX-M6316 in both genotypes. I50values for DPX-M6316 inhibition of ALS activity in extracts from etiolated shoots of A671 and A619 were similar, 15.6 and 17.4 nM, respectively. There was little difference in14C-DPX-M6316 absorption by the two inbreds, but twice as much of the absorbed14C was translocated out of the treated leaf of A619 (13%) compared to A671 (6%). Differences in translocation may have been due to much more rapid DPX-M6316 metabolism in A671 than in A619. Extracts from treated leaves of A671 had only 23% DPX-M6316 remaining 5.5 h after treatment (HAT) compared to 78% DPX-M6316 remaining in extracts from A619 leaves. Therefore, rate of metabolism was the major factor involved in the tolerance of A671 and the susceptibility of A619 to DPX-M6316.