Preliminary results obtained in the evaluation of a mathematical model for flow-injection systems, including chemical kinetics, with an eight-way injection valve are presented. The use of this kind of injection valve permits the insertion of the sample bolus between two different reagent solutions (sandwich techniques). The model considers the system as a tubular reactor with axially dispersed plug flow. As an example for systems with chemical reaction, the enzymatic determination of glucose was chosen. The parameters of the model (dispersion coefficients and reaction rate constants) were experimentally evaluated by using a tracer or by unidirectional optimization, respectively. The effect of different parameters of the flow system on the analytical signal for one analyte and one reagent was simulated, and the model results are compared with experimental data obtained under the same conditions. © 1990.