Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] toxicity, absorption, translocation, and metabolism were investigated in corn (Zea mays L.) and yellow nutsedge (Cyperus esculentus L.). Metolachlor did not inhibit seed germination in corn or tuber germination in yellow nutsedge. It did not kill yellow nutsedge tubers that were exposed to 4 ppmw for 9 weeks. Metolachlor (10 ppmw) applied in soil above the seed significantly reduced corn shoot growth, but the same concentration around or below the seed had no effect. A soil mixture with metolachlor (1 ppmw) placed above or around yellow nutsedge tubers significantly reduced shoot growth, but placement around the tuber was the most toxic; placement below the tuber had no effect on shoot growth. The concentration of metolachlor that resulted in 50% reduction of shoot growth of 4-day-old seedlings in solution culture was > 10−4 M for corn and <10−6M for yellow nutsedge. Root-applied 14C-metolachlor was acropetally translocated to shoots of both species following a 7- to 13-day absorption period, with yellow nutsedge translocating the highest portion of the absorbed material to shoots. In 2-day-old seedlings with roots exposed to 14C-metolachlor for up to 48 h, both species absorbed and translocated the radioactivity to shoots, but corn absorbed much more than yellow nutsedge. When the 14C-metolachlor was applied to shoots of both species, the radioactivity was translocated basipetally into roots. Yellow nutsedge exuded appreciable 14C-metolachlor out of the roots and absorbed more 14C-metolachlor through shoot tissues than corn. Both corn and yellow nutsedge seedlings readily converted the 14C-metolachlor to metabolites, but corn was able to metabolize the 14C-metolachlor at a faster rate than yellow nutsedge and also produced more metabolites.