A newly available commercial instrument, the V&F Instruments (Austria) AirSense 500 mass spectrometer, was evaluated for its ability to measure various hydrocarbons in auto exhaust, in real time. The measurements obtained were compared to off-line high-resolution gas chromatography and other measurement systems during an evaluation period that extended for more than 7 months and involved various Ford vehicle testing facilities. The device was found to provide real-time (1 Hz or faster) concentration data for 10 hydrocarbon exhaust constituents with a precision and accuracy comparable to current off-line gas chromatographic measurement methods. The AirSense 500 was carefully evaluated for its measurement of ethene and other olefins and benzene and other aromatic compounds. The mass spectral measurements agreed, on average within +/-17% of the reported values for the same vehicle tests as measured by offline GC/FID, when comparing the slope of the linear regression line resulting from direct comparison of both techniques. Linear correlations between the two techniques averaged an r(2) of 0.85 for measurements mostly in the 0.01-0.2 ppm range. The instrument was also shown to be useful for the measurement of H2S in dilute vehicle exhaust, at levels down to 20 ppb. In comparison to current methods of H2S measurement, the AirSense 500 was found to be more robust to potentially interfering compounds.