This article is a commentary on the following study: "Short-term associations between fine and coarse particles and cardiorespiratory hospitalizations in six French cities. Host S, Larrieu S, Pascal L, Blanchard L, Declercq C, Fabre P, Jusot JF, Chardon B, Le Tertre A, Wagner V, Prouvost H, Lefranc A. Occup Environ Med, published online Dec. 5, 2007."