When indoor dust particles are heated due to contact with hot surfaces like bulbs, electrical heaters, office equipment, etc., the resulting changes will depend on temperature. One example of this phenomenon is the familiar smell of ”fried dust” when a heater is turned on after the summer season. Awareness of this is not new. In 1924, Hottinger said: ”Settled dust on hot surfaces above 70 degrees Celsius results in distillation products having irritating effect on mucous membranes, fairly equal to the effect of dry air”. We have used GC-MS, SEM, particle counters and TGA to characterize the particulate and gaseous fraction emitted and the residue when various indoor dusts are heated up to 250 degrees Celsius. The Fine particle fraction is of special interest, as newer studies have focused on the surface area of particles - for high adsorption of VOC's as well as determining the exchange area between a particle and a body cell. This seminar will present results from Ph.D. work that is part of an ongoing multidisciplinary project at NTNU entitled ”Indoor environment - health effects of aerosols and settled dust”. The biological component of the project has been delayed due to the birth of twins last summer, but it will continue this fall.