A study was performed to evaluate the soil improvement and stabilization potential of several tropical Hawaiian soils. These improvement techniques included stabilization with locally generated high-quality fly ash, and locally available hydrated lime admixtures. Use of these admixtures has shown tremendous potential as an economical method to upgrade the geotechnical properties of several" poor to marginal" types of tropical Hawaiian soils. The study shows such improvements as increase of unconfined compressive strengths; increases in California bearing ratio (CBR) of more than 10-fold; reduction in plasticity; reduction in swell to less than 10% of the unstabilized values; greatly increased workability; and changes in moisture-density relationships resulting in lower maximum dry densities, higher optimum water content, and less variation of dry density from the maximum over a much wider range of water contents.