Polymer-modified bitumens are very important to the transportation sector. Polyethylene is one of the most used polymers in bitumen modification. The effects of the structural parameters of polyethylene on its dispersion in bitumen and the performance of the resulting polymer-modified bitumens were studied. With the addition of different polyethylenes to bitumen, the performance of bitumen at high temperatures increased as the polymer melt-flow index (MFI) decreased. At low temperatures, the performance of bitumen decreased as the polyethylene MFI decreased. Furthermore, a decrease in the polyethylene MFI intensified its dispersion instability. At very low MFIs, the dispersions were unstable, even under the very high shear forces applied by a double mixer. Moreover, changes in the polyethylene MFI did not improve the dispersion stability at an elevated temperature (165degreesC). (C) 2003 Wiley Periodicals, Inc.