This work investigates the treatability of four different (scotch pine-SP, Siberian scotch pine-SSP, Siberian larch-SL, and oriental spruce-OS) heartwood species with the waterborne preservative copper azole (CBA-A, Tanalith-E 3492). A 2.4% active ingredient solution of CBA-A was applied for use in vacuum/pressure treatment of the heartwood samples. Two different pressure times were used, namely 60 and 120 min. Maximum and minimum penetration values were measured as percentage of cross-sectional area. Penetration of preservative was also determined by X-ray fluorescence spectroscopy analysis (ASOMA). SP resulted in the highest penetration and retention values complied requirements stated in the American Wood Preservers' Association (AWPA) standards. Siberian scotch also showed satisfactory results for standard requirements. SL and OS showed lower penetration and retention results than those of pine samples which can be related to their refractory characteristics. (c) 2006 Elsevier Ltd. All rights reserved.