A program has been initiated in Denmark to investigate the aggressive environment in various waste incineration plants. The results described are the preliminary results from one waste incineration plant. Deposits and corrosion products have been removed from various locations in the boiler. These have been analyzed with respect to morphology and composition using electron microscopy techniques. This results in a map indicating the conditions that exist throughout the plant. This can be compared with a map of flue gas and steam temperatures through the plant and with the amount of corrosion that takes place. Based on this the elements that give rise to corrosion can be identified. In the plant investigated, high corrosion rates were observed where molten chloride salts rich in zinc, potassium and lead were detected.