Recent epidemiological research suggests that short-term effects of particle matter (PM) in urban areas may preferentially be driven by fine fractions. Questions remain concerning the adversehealth effects of coarse particles generated by noncombustion, traffic-related processes and the mechanism of action of PM. Using a time-stratified case-crossover design, we investigated the association between three independent size fractions, coarse (PM10-2.5), intermodal (PM2.5-1), and very fine PMs (PM1), and three health outcomes, respiratory, cardiovascular, and cerebrovascular mortality in Barcelona, Spain, during the period of March 2003-December 2005. Using existing data, we examined the chemical composition of each fraction to explore the effects of PM from different sources and the mechanisms of action. We found that increased levels of PM, and PM10-2.5 were associated with increased levels of cardiovascular and cerebrovascular mortality at lag 1 and lag 2. At lag 1, the odds ratio (OR) for a 1 microg/m3 increase in PM1 was 1.028 [95% confidence interval (CI), 1.000-1.058] for cardiovascular mortality and 1.063 (95% CI, 1.004-1.124) for cerebrovascular mortality. At lag 1, the odds ratio per a 10 microg/ m3 increase of PM10-2.5 was 1.059 (95% CI, 1.026-1.094) for cardiovascular mortality and 1.098 (95% CI, 1.030-1.171) for cerebrovascular mortality. Association with respiratory mortality was only detected for PM2.5-1 at lag 2 (OR, 1.206 per a 10 microg/ m3 increase; 95% CI, 1.028-1.416). Chemical composition data showed that PM in Barcelona was generated in a large proportion by vehicle traffic. Vehicle traffic PM, generated by combustion and noncombustion processes, should be considered in air pollution mitigation strategies in urban areas.