Epidemiological studies have associated the increase of respiratory disorders with high levels of ambient particulate matter (PM) levels although the underlying biological mechanisms are unclear. PM are a complex mixture of particles with different origins but in urban areas, they mainly contain soots from transport like Diesel exhaust particles (DEP). In order to determine whether PM biological effects can be explained by the presence of DEP, the effects of urban PM, DEP and carbon black particles (CB) were compared on a human bronchial epithelial cell line (16-HBE14o-). Two types of PM were used : reference material (RPM) and PM with an aerodynamic diameter < or =2.5 microm collected in Paris with a high volume sampler (VPM). From 10 to 30 microg/cm2, cell viability was never modified whatever the particles. However, DEP and to a lower extent PM inhibited cell proliferation, induced the release of a pro-inflammatory cytokine, GM-CSF, and generated a pro-oxidant state as shown by the increased intracellular peroxides production. By contrast, CB never induced such effects. Nevertheless CB are more endocytosed than DEP whereas PM are the less endocytosed particles. In conclusion, PM induced to a lower extent the same biological effects than DEP in 16-HBE cells suggesting that particle characteristics should be thoroughly considered in order to clearly correlate adverse effects of PM to their composition and to clarify the role of DEP in PM effects.