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 imidazolinone herbicides have been tested in the following in vitro and in vivo genotoxicity studies. In vitro studies are: Microbial mutagenesis in five strains of Salmonella typhimurium, Microbial mutagenesis in one strain of Escherichia coli, Mammalian cell mutagenesis in Chinese Hamster ovary (CHO) cells, Chromosomal aberrations in CHO cells and Unscheduled DNA synthesis in primary rat hepatocytes. In vivo studies are: ominant lethal assay in rats, Chromosomal aberrations in rat bone marrow cells.