The boles of lodgepole pine trees (Pinus contorta murrayana) infected with heartwood decay fungi, emitted ethanol, a potential primary attractant for the mountain pine beetle (Dendroctonus ponderosae), at a higher rate (45.9 mug m-2 day-1) than uninfected trees (19.2 mug m-2 day-1) , on average. The average rate of emission of ethanol by the infected trees was not discernibly different from the average rate of emission of total monoterpenes (32.3 mug m-2 day-1) by these trees. However, the rate of emission of ethanol by uninfected trees exceeded that of total monoterpenes (6.8 mug m-2 day-1), on average. Decay fungi: Perenniporia subacida, Tyromyces sericeomollis and Phellinus pini, were identified in one or more of the decayed trees.