Isoxaflutole is a selective herbicide approved for control of certain broadleaf and grass weeds in field corn and soybean. Isoxaflutole is the first member of a new structural class of herbicides called the isoxazoles. Isoxaflutole works by preventing the biosynthesis of carotenoid pigmentsin both broadleaf and grass weeds. Without carotenoid pigments, chlorophyll pigments are damaged by the sun, and the plant eventually dies. Isoxaflutole is effective against weeds resistant to other herbicide classes such as glyphosate and atrazine. Isoxaflutole was registered conditionally from 1998 to 2004 for weed control in field corn. Isoxaflutole exhibited low acute toxicity via oral, dermal, and inhalation routes of exposure and it is not a dermal sensitizer. In long-term studies via the oral route, isoxaflutole caused ocular toxicity in rats, hepatotoxicity (including liver tumor formation) and thyroid tumors in rats and mice, and hematotoxicity (toxicity to blood) in dogs and mice at high doses. The liver and ocular toxicities observed in rats were consistent with the mode of action of isoxaflutole in mammals (i.e., inhibition of the hepatic enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD)) that leads to a buildup of tyrosine in the blood and the eye.