From 1979 to 1981, the number of ponderosa pines attacked by Dendroctonus valens LeConte was monitored in conjunction with a series of experiments on Dendroctonus brevicomis LeConte. During these experiments, over 100 trees were baited with D. brevicomis pheromone. In four replications, trees baited with pheromone were attacked in greater numbers than were unbaited trees. Thus, I suggest that D. valens is attracted to ponderosa pines by compounds released from the tree during D. brevicomis attack. Alternative explanations are offered.