Many experiments in the literature suggest that the surfaces of colloidal latex particles suspended in water are not smooth. The surface roughness is often referred to as being "hairy". We determined the thickness of the hairy layer on two 5 mu m latex particles by colloidal particle scattering, a new method recently developed by us to measure surface forces. The results are consistent with electrophoretic mobility measurements. The thickness can be determined with an error of 1 nm. Besides the layer thickness, qualitative information about the evenness of the hairy layer can also be obtained. According to our calculations, the stabilizing mechanism under our experimental conditions is related to the hairy layer but cannot be ascribed to steric repulsion. Instead, a layer of immobilized water in the hairy layer effectively lowers the van der Waals interactions, thus increasing the relative importance of electrostatic repulsion. Hamaker constant measurements on the same latex samples indicate that there is no hydrophobic force acting between latex surfaces at separations larger than 28 nm.