Debugging and optimization of extruder performances are often complicated by the lack of transient process data. Most production extruders have excellent process controllers, but they generally lack data acquisition systems. Because of these equipment limitations, all transient, unsteady-state data for a process are unavailable for analysis. Highlighted in this article are four case studies where transient data were collected and used (1) for the diagnosis and elimination of extrusion instabilities; (2) to show differences between competing resin processability; and (3) in extrusion research. In all cases, a portable data acquisition system was temporarily connected to the extruder control panel and was used to collect transient process data. For extruder instability problems, the data collected were used to help diagnose and eliminate the problems quickly, bringing the extrusion lines up to standard production in the shortest possible time, minimizing costly recycle, and maximizing the profits for the processors. (C) 1996 John Wiley & Sons, Inc.