Two on-line tar monitoring devices were operated in parallel on a test gas generation system. The test gas generator applied in this work, is an adaptation of a system introduced by VTT/Finland. Typical aromatic 'tar'species are produced by decomposing ethane in a nitrogen atmosphere at 900 degrees C. By adding steam and toluene to the nitrogen/ethene flow prior to the reactor, the resulting 'tar'-spectrum can be modified. The analytical systems applied were the flame ionization detection based 'FID online - Total Tar Analyzer 300' from University of Stuttgart and Ratfisch Analysensysteme GmbH, and the tar monitoring system based on UV-fluorescence induced by LEDs developed at Technische Universitat Berlin (TUB). The Liquid Quench (LQ) Sampling System, from Paul Scherrer Institute (PSI) was in operation for connecting an on-line micro-GC for continuous monitoring of the permanent gases. Liquid samples for results comparison were taken with the easy to handle 'compact trapping system' (CTS) and were analyzed according to standard methods. The results of this collaborative work proved the applicability of both measurement devices for tar monitoring. Both can follow changes in tar load of the gas immediately. There are differences in response to different `tar'-species distributions which are attributed to the two different basic underlying physical detection principles and the instrument configurations. Applying a simple thermo-chemical reaction system for test gas generation fills a gap between dosing individual tar species into a sample gas and the desired operation of on-line measurement tools at laboratory and industrial scale gasifiers.