The objectives of this project were to develop and test analytical methods that would allow the chemical form (i.e. valence state or compound) of arsenic in drinking waters to be determined, and to use the methods to analyze samples of drinking water from sources where adverse health effects in consumers had been attributed to arsenic. Analytical techniques were developed for the determination of arsenate (differential pulse polarography), for inorganic and organic arsenic compounds (high pressure liquid chromatography with graphite furnace atomic adsorption spectrometry as element-specific detector) and for the detection of arsenocholine, arsenobetaine, and iodoarsines (mass spectrometry). These techniques, inductively coupled argon plasms emission spectrometry, and hydride generation/DC-helium arc emission were used for the characterization of water samples from Utah, Alaska, Antofagasta, Taiwan and Nova Scotia. The total arsenic concentrations were in the range 18 ppb to 8 ppm with arsenic/arsenate ratios between 0.007 and 3.4. No organic arsenic compounds were detected in any of the water samples. The trace elements Al, B, Ba, Ca, Cu, Fe, Li, Mg, Mn, Na, P, S, Si and Sr were present in most of the water samples. The results show that the various physiological effects observed in populations exposed to the arsenic-containing water supplies could not be caused by arsenic compounds other than arsenite or arsenate. Other trace elements acting in concert with arsenite and/or arsenate might produce these symptoms. However, sufficient data are not yet available to evaluate this hypothesis.