Diquat is a dipyridylium herbicide that has been used extensively to control terrestrial and aquatic weeds. Diquat has moderate acute oral toxicity in mammals. Oral LD50 values for various species were between >26 (for dog) and 430 mg diquat (for rat) ion/kg bw. The most notable effects of oral doses were an increase in gastrointestinal water content and hemoconcentration. Diquat has a profound effect on body water distribution; dehydration may play a key role in mortality. The mutagenic potential of diquat was studied in a number of bacterial and eukaryotic systems. The results reported in the literature are contradictory. No antifertility or teratogenic effects were observed in mice, rats, or rabbits after oral diquat administration. However, teratogenic effects were observed when diquat was administered to rats and mice via intraperitoneal (ip) or intravenous (iv) injections.