In treatability trials, radiata pine heartwood and sapwood samples were treated with copper-chromium arsenic (CCA) preservative under vacuum pressure. Of the 40 heartwood samples, only 10 percent had permeabilities outside the limits which would be accepted as normal for a charge of uniform material. A high content of resinous extractives was a major cause of impermeability, but wood structure was also a factor. In laboratory decay tests, heartwood showed low natural durability. However, heartwood blocks treated with CCA to retentions equivalent to those in the outer 13 millimeters of test stakes suffered no weight losses in laboratory decay tests even though some had retentions which would not have been expected to prevent decay in similarly treated sapwood. Field testsconfirmed the low average durability of heartwood. Treatment with CCA significantly increased decay resistance. Natural durability can supplement low preservative retention to provide resistance to decay. -- AATA