A series of colloids based on poly(styrene) were prepared by emulsion copolymerization with various proportions of methacrylic acid. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to monitor changes in particle surface composition and indicated a substantial enrichment of the methacrylic acid component. Further evidence for the presence of carboxyl groups at the particle surfaces was provided by electrophoretic mobility measurements, which showed a marked increase over the pH range studied.