Propetamphos ((E)-O-2-isopropylcarbonyl-1-methylvinyl-O-methylethyl phosphoramidothioate) is an organophosphate pesticide (OP) and has been used as an active ingredient in sheep dip where there is the potential for significant dermal exposure during dipping. Biological monitoring of exposure to propetamphos has until recently relied on the measurement of cholinesterase activity in plasma. Following the development of a novel method for the determination of propetamphos metabolites in urine, it is now possible to biologically monitor exposure using urine samples. This paper describes a human volunteer study involving oral and dermal exposure to propetamphos.