The paper deals with the modelling of the flow of liquid in a compartment of continuous dialyzer. Two simple models, the dispersion model and tanks-in-series model, were used. Their parameters Peclet number, the mean residence time of liquid in dialyzer compartment, the number of tanks and the mean residence time of liquid in each tank were determined from a nonideal step input of a tracer and its response. It has been found that in the range of the Reynolds number from 0.44 to 3.64, the Peclet number and the number of tanks are in the range from about 200 to 320 and from 100 to 310, respectively. Both these parameters and the mean residence time of liquid in the compartment of dialyzer and in each tank decrease with the increasing Reynolds number. Furthermore, it has been proved that the values of the mean residence time of liquid in the compartment of dialyzer calculated from the dispersion model agree well with those calculated from the tanks-in-series model. The obtained values of the Peclet number and the number of tanks indicate that the how-in the dialyzer does not significantly differ from the plug flow.