Concentrations of arsenic have been measured in soils, streambed sediments, ground water, surface water, and drinking water in New Jersey over the past few decades as part of several U.S. Geological Survey (USGS) and other agency investigations with various objectives. Results of these studies indicate that arsenic concentrations vary spatially in all the sampled media and that both natural and human sources of arsenic in the environment may affect drinking-water quality. Arsenic concentrations in ground water, surface water, and drinking water rarely exceeded the previous Federal and State Maximum Contaminant Level (MCL) of 50 µg/L (micrograms per liter); however, the new Federal MCL of 10 µg/L will be exceeded in several public and many domestic drinking-water-supply wells in New Jersey. Arsenicconcentration data for environmental samples in some parts of New Jersey are scarce. Additional data as well as process-related studies will help to determine which human populations are most likely to be exposed to arsenic.