Solutions of poly(N-isopropylacrylamide) (PNIPA) with added sodium dodecyl sulfate (SDS) were investigated by light scattering methods at temperatures of 15-40 degrees C. The formation of well-defined nanoparticles of PNIPA was observed on heating at low SDS additions. The effects of PNIPA and SDS concentrations and the molecular weight of PNIPA on nanoparticle parameter were investigated. An interpretation based on stabilization of PNIPA nuclei by SDS was suggested.