An experimental setup was built for the characterisation of residence time distribution (RTD) in microreactors. In order to determine the residence time distribution of those devices, the method of pulse marking with a dye tracer was used. For this method of marking, a specially constructed microstructured injection unit came to use. Detection of the tracer concentration was made by analysing the transmittance with a self-developed transmittance detection unit. The obtained residence time distributions were compared with common RTD models by means of fitting methods. The examined static micromixer showed laminar flow behaviour. (C) 2004 Elsevier B.V. All rights reserved.