We investigated the hypothesis that wood-boring beetles in the genus Monochamus (Cerambycidae) utilize pheromones of sympatric bark beetles as host-finding kairomones. All nine bark beetle pheromones tested electrophysiologically were antenally active for both sexes of M. scutellatus, M. clamator, and M. obtusus from British Columbia. When field-tested with multiple-funnel traps (British Columbia) or cross-vane traps (Ontario), a blend composed of frontalin, ipsdienol, ipsenol, and MCH, in combination with a blend of host volatiles attracted significant numbers of M. clamator, M. obtusus, M. notatus, and M. scutellatus to baited traps. Traps baited with host volatiles in combination with a second blend composed of endo-brevicomin, exo-brevicomin, cis-verbenol, trans-verbenol, and verbenone caught no more beetles than unbaited traps or traps baited with the host blend alone. In British Columbia, traps baited with the first blend alone or both blends together captured more M. scutellatus and M. clamator than unbaited traps, demonstrating a response to bark beetle pheromones in the absence of host volatiles. These results suggest that Monochamus spp. are minimizing foraging costs by using the pheromones of sympatric bark beetles as kairomones.