Polymer-modified binders are increasingly used by the pavement industry. In practice, the bituminous binders are stored at high temperatures previous to its application on the road. The instability problems of the bitumen due to the polymer-rich phase separation may affect the final properties of the pavement. Most polymers tend to be insoluble, to some degree, in the bitumen matrix, and phase separation may result. Chemical compatibility between the polymer additive and the bitumen, and processing conditions, are crucial to obtain suitable properties of the polymer-modified bitumens. In this work, different polymer-modified binders were manufactured by using a high-shear mixing device. Once a good mechanical dispersion of the polymer in the bitumen matrix was achieved, the binders were stored in tubes at high temperatures. During the storage, the unstable polymer-rich phase segregates and starts to ascend up to the surface. The progression of the polymer phase separation was followed through the evolution of the linear viscoelastic and the viscous properties of the samples collected, after different storage periods, from the top part of the storage tube. From the experimental results obtained, we may conclude that the use of a reactive polymer as additive is a promising alternative to obtain more stable binders. (c) 2006 Wiley Periodicals, Inc.