Preservative-treated and modified wood may behave differently to untreated wood, especially the properties related to the corrosion of fasteners. The main reasons for this are that preservative, treated and modified wood contain chemicals that can increase corrosion and that such wood is often used in constructions where exposure to rain or moisture is an issue. The aim of this study was to investigate the effect of thermally treated timber (TMT)* on the corrosion of different types of fasteners in comparison with untreated wood. The study was part of a series of investigations of properties of TMT that SP Technical Research Institute of Sweden initiated in 2001 with financial support from the Swedish Wood Association (Jermer et al 2003). Progress reports have been published in 2005 (Jermer and Andersson 2005) and 2012 (Jermer and Andersson 2012).