Inflammatory response is implicated as a biologic mechanism that links particulate matter (PM) air pollution with health effects. C-reactive protein (CRP), an important acutephase reactant with profound proinflammatory properties, is used clinically as an indicator of the presence and intensity of inflammation. In vitro and in vivo animal studies suggest that CRP levels increase in response to PM exposure, but there was no consistency in epidemiologic studies. Herein, a systematic review was conducted to examine the association between PM exposure and serum CRP levels in humans. Elevated CRP levels were consistently found among children, and CRP elevations were also observed among healthy adults, albeit requiring higher peak levels of PM exposure. PM-induced CRP responses were not consistently found in adults with chronic inflammatory conditions, perhaps because of the use of anti-inflammatory medications in this population. Of the eight examined randomized trials, only one trial with a longer intervention period supported the effect of PM exposure on CRP concentrations. To provide conclusive evidence, further epidemiologic studies are needed to better quantify the magnitude of CRP level changes in response to PM with well-defined study populations and better control of various confounding factors.