A series of 5 studies in a total of 300 middle-aged and elderly individuals have related exposure to indoor and outdoor ultrafine and fine particles for 5-48 h to effects on vascular and lung function with possible explanatory inflammation and oxidative stress biomarkers. The data consistently support detrimental effect of UFP from traffic on vascular function. Indoor UFP and PM 2.5 might contribute to cardiovascular risk through endothelial damage and vascular dysfunction, respectively, whereas indoor UFP dominated by candle burning appears to have adverse lung effects. The biomarkers provided no mechanistic explanation.