Several chemical compounds that are widely distributed in the environment have been found to possess hormone-mimicking activities. These compounds have been found to interfere with hormonal activity through a variety of mechanisms, and they may have adverse effects on the health of animals and humans. Terms used to describe these compounds include endocrine disruptors, hormone disruptors, and estrogen mimickers. Classes of compounds believed to have hormone-disrupting effects include phthalates (plasticizers), alkyphenols (detergents), organochlorine pesticides, PCBs, dioxins, and food packaging chemicals such as bisphenol A (BPA) and butylated hydroxyanisole (BHA). Efforts are underway in several countries to develop analytical methods for assessing the distribution of these compounds in the environment. In the US, the Environmental Protection Agency has established the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC), and in Japan, the Environment Agency has organized the Environmental Endocrine Disruptor Group. We report the analysis of ppb-level samples of standard samples, river water and water from sewage treatment plants by both low-and high-resolution selected ion moniroting (SIM) mass spectrometry with benchtop GC/MS systems. We evaluate high- and low-resolution SIM with LC/MS methods as an alternative analytical approach that does not require derivatization.