Phoxim (Diethyl-O-(alpha-cyanobenzylideneamino)-thiophosphate) is an organophosphorus insecticide used in veterinary medicine for the control of mites, lice and other ectoparasites in cattle, pigs, sheep, and goats. Phoxim is also used for plant protection, in tea production. The insecticidal activity of phoxim is mediated through inhibition of cholinesterase. Phoxim is an insecticide with selective properties: it is toxic to insects but virtually non-toxic to mammals. Although differences in sensitivity to cholinesterase inhibition contribute to this selectivity, metabolism plays a more important role. In both insects and mammals, phoxim is oxidatively desulfurated to the oxo-analog, PO-phoxim, which is a more potent inhibitor of cholinesterases than phoxim itself. In mammals, however, PO-phoxim is an extremely short-lived intermediate and, together with phoxim, is rapidly hydrolyzed to non-toxic products.