As a first step in a hierarchical scheme to demonstrate the suitability of present U.S. Environmental Protection Agency (USEPA) analysis methods and/or develop new methodology, the gas chromatographic (GC) separation and mass spectrometric (MS) detection characteristics of 328 toxic and/or hazardous organic materials have been investigated. Volatile and semivolatile analytes were tested using the GC/MS conditions specified in the USEPA Methods 8240 and 8270, respectively, as modified by the Contractor Laboratory Program (CLP) protocol. Standard mixtures of analytes were analyzed by septum injection onto the analytical column without any prior sample work-up procedures. For the 187 analytes that proved suitable for GC/MS analysis by Methods 8240 and 8270, the relevant characteristics for GC retention (retention time and relative retention index) and for MS detection (recommended quantification ion and confirmation ions with relative abundances and response factor relative to the internal standard) are reported. For analytes not detected by GC/MS or not included, a priori, recommendations for future work are made.