Information about polydisperse colloidal systems was obtained by dynamic light scattering. The correlation functions obtained were analyzed by the histogram method and the method of cumulants. The former was, as a test, applied to a nearly monodispere polystyrene latex. The agreement between the obtained results and the values given by the supplier was rather good. Therefore, this technique was applied to some nonionic microemulsions to determine their particle size distribution. The results obtained were in agreement with our rheological measurements on these systems published previously. The cumulant method was used to follow the diffusion coefficient of the dispersed particles in microemulsions as a function of temperature.