A novel membrane inlet mass spectrometer is used to monitor organic compounds in combustion emissions. Different gas probes, which can be changed in minutes, have been developed for use in combination with the mobile mass spectrometer. With the On-Line-Probe, volatile organic compounds (BTXE) can be measured down to the ppm range with a cycle rate of one analysis per second. Time resolved measurements of aromatic compounds together with other exhaust gases can be done. By sampling with a polymer adsorbent, analysis with thermal desorption and GC/MS down to the ppb concentration range can be achieved. A six-fold Tenax-Sampler, connected to the mobile GC/MS system, is capable of taking and transferring the samples automatically. Because sampling with this device is independent from the analysis, measurements of narrow time windows in a dynamical process can be done easily.The whole analytical equipment was evaluated on-site through measurements on an engine test stand, a dynamometer and “on the road” during real traffic. It is shown, that time resolved quantitative measurements give information on the influence of special driving conditions (warm up, congestion) on the amount of aromatic compounds emitted by automobile exhausts.