Starting from our previous results concerning the melt flow during the dispersive mixing zones of Maddock and Egan type, one establishes relations for the pressure variation, appropriate for incremental calculation. Because generally the melt flow along the mixing zone is non-isothermal, one establishes relations for the temperature variation along the mixing zone, namely: temperature variation caused by, external heating, by internal friction, by external friction and due to melt compressibility. By using the established relations one develops a network procedure for pressure and temperature variation calculation along the mixing zone. The computer program based on the network procedure was used to calculate a usual mixing zone for a 63.5 mm extruder-screw. The program gives the possibility to represent the pressure and temperature variation between the inlet and the outlet of the mixing zone. This is useful when we are interested in the optimum design of such mixing zones.