In 2000 and 2002, Verbenone, a compound with anti-aggregation properties for mountain pine beetle, Dendroctonus ponderosae, was tested for reducing attacks by the insect in Ponderosa pine, Pinus ponderosae forests. The verbenone was released to the environment with the use of permeable membranes; the first year with plastic capsules (containing 0.8 g of verbenone) and the second year with an envelope-like pouch (containing 5.0 g of verbenone). The plastic capsules were deployed at a rate of 25 and 64 capsules per acre and a no capsule treatment served as control. The pouches were deployed at 30 and 50 pouches per acre and a no pouch treatment was the control. Mountain pine beetle attractants were placed on three trees at plot center to ensure insect population pressure. In neither experiment were there any observed differences in (1) number of mountain pine beetle-killed trees, (2) number of partial attacks (strip attacks), (3) number of unsuccessful attacks (pitch-outs), (4) diameter at breast height of infested trees, (5) attack height of infested trees, (6) mean distances of infested trees to verbenone releasers, (7) attractants located at plot center. The possible influence of stand environment is discussed as reason for lack of effectiveness. At this point, based on this and prior studies the operational use of verbenone for reducing mountain pine beetleattacked trees in ponderosa pine forests is not advisable. Further studies on this topic should be conducted in the future as treatment technology is developed further or the appropriate release amount and timing is better understood.