Unbound aggregate bases serve a major structural component of most flexible pavement systems. This paper describes the performance of highly stabilized aggregate systems as unbound base layers with four content levels of non-plastic fine materials. Each system is characterized in terms of vertical and horizontal resilient moduli and cumulative permanent deformation. Resilient moduli are determined over a range of 10 stress states in at optimum molding moisture and at a high moisture content (approaching 90 percent saturation). In the high fines blends, the stiffness increase due to the chemical additive is in the order of 50 to 75 percent (still in the range of "flexible"bases), the level of anisotropy is substantially reduced and the predicted performance of the entire pavement system based on finite element analysis showed significant improvements. The paper demonstrates that high fines unbound bases modified by low levels of chemical additives have attractive economic and performance characteristics.