The influence of wood extractives such as free fatty and resin acids, pinosylvin, steryl esters and triglycerids in sapwood, heartwood and induced lightwood of Scots pine, Pinus sylvestris L., on decay resistance against Postia placenta and Phanerochaete chrysosporium was investigated. After incubation periods of 38 and 42 days for the brown and white rot, respectively, the wood blocks were weighed and the weight losses of the blocks were correlated to the chemical composition of the wood types. Both fungi decayed the sapwood at a greater rate than they did the heartwood and the lightwood. - If the weight losses are compared to the chemical composition it is obvious that the losses caused by both fungi are lower in the wood tissues with high levels of pinosylvin and/or resin acids. It was concluded that pinosylvin alone cannot be responsible for decay resistance in the heartwood and the lightwood. Most probably resin acids are also important factors in decay resistance in the heartwood and the lightwood. Most probably resin acids are also important factors in decay resistance because they act as waterproofing layers thus retarding the entrance of the decay fungi. - The results from the present work also suggest that triglycerides are important factors in wood decay. In wood with low decay resistance triglycerids accounted for 60-70 % of total lipids while the corresponding value for those with high resistance was about 1 %. Obviously the inhibitory effects of pinosylvin and resin acids might be overcome if nutrients like triglycerides are available in the wood.