As a result of its potential as an added-value, environmentally acceptable, high performance wood product, borate-treated lumber has attracted the interest of the Canadian forest products industry (Byrne 1990). One of the potential markets for borate-treated wood in Europe and North America is millwork. Currently millwork manufacturers use light organic solvent preservatives to provide durability to their products but there are a number of reasons why this situation may change in the near future. There are increasing pressures on uncontrolled emission of volatile organic solvents from treated wood and public concerns regarding some of the active ingredients now in use (Orsler and Holland 1993). The use of borate-treated wood eliminates both of these problems and may provide some additional advantages by eliminating batch processing in the manufacture of joinery. The one factor which is likely to have the greatest impact on the performance of borate-treated millwork is the mobility of the boron. Borate-treated wood is currently approved for use in exterior exposure in New Zealand provided it has a three-coat paint finish. Nevertheless there is concern outside New Zealand that redistribution of boron within the treated wood could lead to localized depletion and decay. An L-joint test of borate-treated wood was set up by Forintek to determine whether preservative depletion and subsequent decay is likely to be a problem. This report describes the performance results of this trial after six years and compares borate content of the L-joints initially and after five years exposure.