This part of EN 351 gives guidance on the general procedures to be used in obtaining samples of preservative-treated wood for the determination of penetration and retention of wood preservative. It also gives guidance on how to measure the penetration and retention of a wood preservative in the treated wood. This part of EN 351 is applicable to the production of preservative-treated solid wood, including glued laminated timber, suitable for use in those service conditions defined by the use classes in EN 335. This part of EN 351 is not applicable to preservative-treated wood in service. However, the sampling guidance provided within this part of EN 351 can be applied for the subsequent examination of treated wood in service. Annex A (informative) provides a selection of number of sampling units. Annex B (informative) provides examples of retention measurements.