GC-MS methods have been developed which provide either analysis of eleven halocarbons in ambient air samples or only rapid analyses of CH3CI and CH2CI2, two species for which GC-ECD is particularly insensitive. Detection limits and precision of analysis for the remaining species are generally not as good as with GC-ECD, but the methods provide separate checks for more certain identification of the particular species of interest. In addition, the methods exhibit more uniform sensitivity for all of the halocarbons, and the GC oven can be temperature-