Epidemiological studies have shown commuting in traffic is associated with adverse health effects. It is vital to assess commuter exposure to traffic-related air pollutants before considering potential health risks; however, there are relatively few publications considering commuter personal exposure in China. The authors conducted a field study to measure commuter personal exposure to particulate matter e2.5 ím in aerodynamic diameter (PM2.5) and CO in 3 commuting modes in Beijing. PM2.5 and CO personal concentrations and whole trip exposures were compared among the 3 commuting modes. After controlling confounding factors, it was determined that taxi commuters were exposed to lower PM2.5 concentrations (31.64 ( 20.77 íg/m3) versus bus commuters (42.40 ( 23.36 íg/m3) and cyclists (49.10 ( 26.60 íg/m3). CO personal concentrations were significantly higher when commuting by taxi (5.21 ( 1.52 ppm) versus bus (2.41 ( 0.99 ppm) and bicycle (1.90 ( 0.55 ppm); however, when inhalation rates and trip duration were considered, cyclists experienced the highest whole trip exposures to PM2.5 and CO (p <0.05). Fixed site monitoring data were not appropriate surrogates for personal exposure while commuting, particularly during heavy traffic. The authors concluded that PM2.5 and CO personal concentrations were greatly affected by the commuting mode. Highest whole trip exposure to PM2.5 and CO experienced by cyclists indicated it is not preferable to commute by bicycle in a relatively high air polluted environment. Cyclists were possibly subject to greater health risks than other commuters. The authors concluded that additional research must be conducted to assess health risks associated with cycling.