Abstract An experimental investigation was carried out in order to test the suitability of fluid-dynamic models for the interpretation of data for multistage mixer columns of the RDC and Mixco types. Mean local concentration values in the inside of the compartments were measured and experimental impulse response curves were systematically compared with the theoretical curves corresponding to the models. Furthermore the results of static and dynamic methods of measurement of model parameters were compared. In order to bring out possible causes of error due to buoyancy phenomena, feed was introduced either into the bottom stage (ascending flow) or the top stage (descending flow). Local inspection and comparison of experimental and theoretical dynamic curves as well as results of different methods for measuring the amount of backmixing confirm the great reliability of the model of a cascade of ideal tanks with backmixing for the systems considered.