The imidazolinone herbicides have been subjected to exhaustive toxicological studies to determine their toxicities to mammals and other nontarget organisms and to evaluate the potential hazard of handling and applying these herbicides. As demonstrated by the results of those studies, the imidazolinones have a low toxicologic potential, partially because they act by inhibiting a biosynthetic process at a site present only in plants. In addition, these herbicides are excreted rapidly by rats before they can accumulate in the tissues or blood. The results of these studies are presented below.