A field demonstration of portable mass spectrometers was held at two hazardous waste sites. These demonstrations were sponsored by the Consortium for Site Characterization Technology (CSCT) as part of the U.S. Environmental Protection Agency's (EPA) Environmental Technology Verification (ETV) program. The demonstrations were held at the DOE Savannah River Site, Aiken, South Carolina in July 1995 and at Wurtsmith Air Force Base in Oscoda, Michigan in September 1995. Instruments demonstrated included the Bruker-Franzen Analytical EM640(TM) mobile gas chromatograph/mass spectrometer, the Teledyne Electronic Technologies 3DA(TM) Discovery ion trap mass spectrometer with a direct injection inlet system and the Viking Instruments Corporation SpectraTrak 672(TM) transportable gas chromatograph/mass spectrometer. The demonstration was designed to evaluate whether the instruments met the developers' performance goals for a variety of media and analytes under field conditions. At each location, samples of soil gas, ground water, and soil were analyzed for volatile organic compounds. Split samples were analyzed by standard analytical methods at commercial laboratories to provide a reference for verifying the performance of the instruments.