The supercritical solution rapid expansion technique, rapid expansion of a supercritical solution into a liquid solvent (RESOLV), was applied to the processing of poly( L-lactic acid) and poly( methyl methacrylate) into nanoscale particles ( 100 nm or less). Neat supercritical carbon dioxide or with ethanol as a cosolvent was used as solvent, and an aqueous medium was used at the receiving end of the rapid expansion. The as-produced polymeric nanoparticles were suspended, and various strategies for the stabilization of the suspension to protect the nanoparticles from agglomeration were evaluated. It was found that, in the presence of a water-soluble polymer or surfactant, aqueous suspensions of the well-dispersed polymeric nanoparticles could remain stable for an extended period of time to allow potentially further processing into the desired products.