Sapwood blocks (5 x 2.5 x 0.5 and 15 x 2 x 2 centimeters) of beech and Scots pine were impregnated with copper-chrome-arsenic (0, 3, 6 or 10%) and immersed in Galway Bay off the western coast of Ireland. Fungal colonization, weight loss, and microdistribution of copper-chrome-arsenic were determined after 3-12 months. Fungi colonized untreated blocks within three months, but were generally absent from treated blocks after 12 months. Untreated small blocks of beech and pine showed weight losses of 45.6 and 34.5%, respectively, after 12 months. Weight loss of untreated larger blocks was moderate (10.3 and 6.1%) after nine months, while weight loss of all treated blocks was less than 4%. Tables and bar charts show the microdistribution of copper, chrome, and arsenic as determined by scanning electron microscopy in conjunction with energy dispersive x-ray analysis. Rays and pit membranes of both woods retained high preservative contents after submersion, but beech fibers had low contents of preservative. Chrome and arsenic were leeched more than copper. -- AATA