Wood extractives can be envisaged to protect heartwood by at least three different mechanisms, i.e. fungicide, free radical scavengers/antioxidants and as metal chelators. In short-term laboratory decay tests using two different wood species and decay fungi, the combination of different organic fungicides with various antioxidants and/or metal chelators gave enhanced activity as compared to the organic biocide alone, with the best results usually obtained with all three compounds. Outdoor ground-contact stakes treated with a biocide and antioxidant combination and exposed for 30 months also gave enhanced protection against both decay fungi and termites. It was concluded that the combination of an organic biocide with metal chelating and/or antioxidant additives gives enhanced protection to wood against fungi as compared to the biocide alone and, consequently, it may be possible to develop environmentally-benign wood preservative systems based on this idea.