Attraction of the spruce beetle, Dendroctonus rufipennis (Kirby), to beetle-infested logs was reduced 99% by addition of 3-methyl-2-cyclohexen-1-one (MCH), the natural antiaggregative pheromone of the Douglas-fir beetle, D. pseudotsugae Hopkins. The synthetic attractant frontalin and α-pinene attracted few spruce beetles and its nominal attraction was nearly nullified by addition of MCH. Male spruce beetles responded to the natural and synthetic attractants in greater numbers than females. When MCH was added to these treatments, females predominated among the few beetles caught. The clerid Thanasimus undatulus Say was strongly attracted to treatments containing frontalin, whether or not MCH was added, but MCH alone was not attractive to this predator. Among 13 other species of scolytids caught, the most abundant were Scierus annectens Leconte and Hylastes nigrinus (Mann.). Two relatively rare species, Scierus pubescens Sw. and Xylechinus montanus Blkm., were attracted in unusual numbers to natural spruce beetle attractant. Intensive study is recommended of the possible use of MCH to prevent increase of spruce beetle populations.