An ammoniacal preservative, copper-zinc-arsenic-additive (developed at the Eastern Forest Products Laboratory for difficult-to-treat wood species), was tested in a commercial treating plant using poles, posts, and lumber of white spruce (Picea glauca [Moench] Voss). The treatment schedule comprised steaming for 5 hours followed by a standard full-cell treatment with a solution containing 2.2 percent oxides and 6 percent ammonia heated to 35C (95F). A pressure near 860 kPa (125 pounds per square inch) was maintained for 10-15 hours.