A process control concept for peroxide-initiated degradation of polypropylene was presented. The link-up of a twin-screw extruder to an on-line Rheometer and a computer system using a newly developed program package can he used to form a process control system unaffected by external disturbing influences and leading to a long-term constant product quality. Work is still to be done concerning development and optimization in the area of layout and design of adapter systems and concerning the measures for lowering the controllability ratio Z1 Special attention should be given to a processing concept to enable changes in M̅w and MWD independently of one another.