H-1 NMR is found to be a suitable method for determining the adsorption of the nonionic surfactant Triton X-405 on polystyrene particles dispersed in D2O. In the NMR spectra, free Triton X-405 and Triton adsorbed on the surface can be easily distinguished because of the different chemical shifts, Free Triton appears at 3.6 ppm, whereas adsorbed Triton shows a signal between 3.48 and 3.53 ppm, depending on the orientation of the molecules on the surface. At low concentration, the Triton X-405 chains lie relatively hat on the surface, leading to a broad signal and the lowest chemical shift. With increasing Triton X-405 concentration, the signal shifts to higher chemical shifts and becomes narrower due to a decrease in the area occupied by a chain. These experiments allow the characterization of the detailed partitioning of the Triton X-405 in the water phase and on the particles, This leads to the determination of the adsorption isotherm, The value determined for the area occupied by one molecule of Triton X-405 is 172 Angstrom(2), and the adsorption equilibrium constant, b, is 3.8 X 10(5) dm(3) mol(-1).