A new class of reactive polymer modifiers designed to improve binder-aggregate adhesion in asphalt concrete was evaluated. Using a controlled free radical polymerization process, polyisoprene was prepared with short blocks of reactive amino- or silane-functional monomer at one end of the polymer chain. The reactive polymers so synthesized were tested with a modified version of the Tunnicliff-Root method (ASTM D4867) for measuring retained tensile strengths after water immersion moisture conditioning at 60 deg C for 24 h. It has found that the retained tensile strength of the unmodified samples was 53%, and the retained tensile strength of the regular polyisoprene-modified control samples was between 57 and 69%, depending on the polymer molecular weight and content. The best retained tensile strengths of 86 and 90%, respectively, were obtained with samples modified with 3 and 5% by weight of the higher-molecular-weight silane-functional polyisoprene. The method for obtaining the desired effect is flexible; lower-cost monomers, such as butadiene, and more common polymerization methods, such as emulsion or anionic polymerization techniques, may be used equally well to produce polymers with similar or better performance characteristics. An added benefit is that the tested polymers imparted significant improvements in low-temperature performance measured with the thermal stress restrained cooling test.