Mixed dispersions of anionic polystyrene latex and cationic microgels of poly(N-isopropylacrylamide) coexist as colloidally stable mixed dispersions at 20 degrees C. However, at elevated temperatures (50 degrees C) a heteroflocculation of the dispersion takes place within certain concentration ranges of microgel particles. The system redisperses on cooling, but only at elevated pH values.