Ammoniacal wood preservatives have been known for many years and are considered among the best water-borne systems for protecting wood in ground contact. In recent years attention has been increasingly focussed on these preservatives because of their ability to penetrate difficult-to-treat species better than most other fixed water-borne preservatives. This is particularly important for example, in eastern Canada, where there is an abundance of spruce and a relative shortage of easily treated woods such as pine. Besides being able to readily penetrate wood, the preservative must also be well fixed in the wood. We have concentrated in recent years on improving the already good fixation of ammoniacal copper arsenate and have paid particular attention to increasing the ratio of copper ions to arsenic ions, adding extra anions, and also substituting all or part of the copper by zinc. The preservatives thus formulated are termed copper arsenic additive (CAA), copper zinc arsenic additive (CZAA) and zinc arsenic additive (ZAA). Many of the properties of these preservatives have been reported elsewhere (Hulme, 1979). However, no reports have yet been prepared on their ability to protect wood in sea water. This first progress report indicates how well these preservatives protect wood against marine borer attack in Canadian coastal waters for at least 8 months.