Serpula lacrymans causes wood decay, which is of major economic importance in many areas of the world and in the U.K. alone £400 million pounds worth of damage is caused on an annual basis. Conventional treatment regimes for wood decay caused by the wood decay basidiomycete Serpula lacrymans involve the removal of infected timber, the removal of non-infected timber around the infection site and the use of powerful fungicides. Depending upon the scale of the infection the treatment can be expensive and misidentification of the fungus causing the decay is not unknown. Health and environmental problems can arise with the use of the fungicides and removal of timber, in particular that of historical or artistic value, is not always desirable. Biological control of wood decay fungi has been proposed for a number of years and previous investigations have indicated that control of decay fungi is possible. However, there were a number of problems reported, in particular, the extrapolation of the laboratory work into the field situation. It has been shown that Trichoderma isolates are antagonistic towards S. lacrymans on several media types and wood, with wood colonised initially by Trichoderma isolates resistant to infection by S.lacrymans. Screening experiments, carried out on different media and wood, provided a Trichoderma isolate that would be used in the medium-scale and field trial experiments. The screening experiments indicated that nutrient composition is important for the effectiveness of the Trichoderma isolates, with a high nitrogen level increasing the antagonistic effectiveness. Through the development of a small scale wood interaction system it was determined that certain Trichoderma isolates could prevent the decay of wood by S.lacrymans. However, the S.lacrymans developed specialised hyphal structures (strands) to bypass the Trichoderma colonised portions of the wood. The medium-scale and field trial experiments indicated that Trichoderma could be used to protect wood from decay and prevent the spread of S.lacrymans. However, the existing S.lacrymans colony could not be killed although it could be induced to produce fruit-bodies by the direct application of the Trichoderma to the S.lacrymans. A PCR system was developed to detect the spread of both S.lacrymans and Trichoderma through wood. Although the Trichoderma could not be detected, the S.lacrymans could be detected in wood sections not visually infected with S.lacrymans. Extracellular enzyme studies indicated that the phenoloxidase enzyme laccase was important in the defensive strategy of S.lacrymans and in the offensive strategy of Trichoderma isolates. These studies also showed that S.lacrymans may use laccase as a general stress enzyme as laccase was detected during antagonistic, nutritional and temperature stress situations.