BACKGROUND: Carbonaceous and metallic components of particles have been shown to play a role in particles\' effects on cardiac autonomic function as measured by heart rate variability (HRV). Previously we reported the association of HRV with marked changes in traffic-related particulate air pollution around the Beijing 2008 Olympic Games in a panel of taxi drivers. OBJECTIVE: We further investigated the relationship between exposures to the carbonaceous and metallic components of traffic-related particles and HRV in the same population. METHODS: Repeated measurements of in-car exposures to particulate matter </= 2.5 mum in aerodynamic diameter (PM(2).(5)), carbon monoxide and nitrogen oxides were conducted in a group of 14 taxi drivers for one work shift in four study periods around the Beijing 2008 Olympics. The quantities of organic/elemental carbons and 27 elements of the in-car PM(2).(5) mass were determined laboratorially. Linear mixed-effects models were used to evaluate the impact of exposures to different PM(2).(5) components on HRV while controlling for potential confounders. RESULTS: Taxi drivers\' exposures to in-car PM(2).(5) and its components showed dramatic changes across the four study periods around the Beijing 2008 Olympics. Differences in associations of in-car PM(2).(5) components with HRV were found. An interquartile range (IQR: 917.9 ng/m(3)) increase in calcium was associated with a 5.48 millisecond [ms, 95% confidence interval (CI): 0.71, 10.24] increase in standard deviations of normal-to-normal (SDNN) intervals, while an IQR (4.1 ng/m(3)) increase in nickel was associated with a 1.53 ms (95% CI: 0.14, 2.92) increase in SDNN index. Additionally, a decline of 8.11 ms (95% CI: -15.26, -0.97) in SDNN per IQR (481.4 ng/m(3)) increase in iron was also found. CONCLUSION: The results support associations of PM(2).(5) metallic components with HRV in younger healthy individuals. Future studies are needed to clarify the interaction among different PM(2).(5) components or the role of PM(2).(5) mixtures.