Because of recent air pollution laws, there is need of an accurate mobile hydrocarbon analyzer. Measurement of so-called 'non-methane hydrocarbons' was carried out in a mobile laboratory using a flame ionization detector. Total hydrocarbons were measured by running air directly through the detector. Methane was measured by running air through a methane-saturated carbon column which retained all organic contaminants other than methane. The difference was then the 'non-methane hydrocarbons.' Bag sampling may be superior to continuous monitoring, depending on circumstances. Sensitivity appears to be marginal in view of the federal standards. The method is subject to error due to difficulties in calibration, temperature control, and other variables. (Author)