A melt flow indexer (MFI) was used to investigate high-temperature transitions in melts of high-density polyethylene (HDPE). The MFI data were obtained in the range 190-230degreesC. These transitions were found in the MFI at about 210 and 225degreesC and reproduced in a Haake melt blender. Polystyrene was used in the blender experiment to demonstrate typical amorphous behavior. For HDPE melts, the MFI-temperature behavior and the torque-temperature data of the blender were found to be alternative images of the same anomalous temperature dependency in the range 210-225degreesC. Also, the Haake melt blender was able to reproduce the 150degreesC transition observed by Kolnaar and Keller in the extrusion of HDPE. Regardless of the simplicity of the MFI device, results are in agreement with our previous DSC findings. (C) 2003 Wiley Periodicals, Inc.