The objective is to determine whether moderate exposure to particles from wood smoke in a real life situation causes an systemic inflammatory response in peripheral blood or in lower airways. 24 healthy subjects (normal healthy subjects and mild asthmatics to study the asthmatic response) is selected for the study. A randomized double blind crossover procedure will be followed with a PM exposure concentration of 200ug/m3, 400ug/m3 or clean air as the control exposure. Exposure will take place in a climate chamber using wood burning in an appropriate wood stove.