The mountain pine beetle, Dendroctonus ponderosae Hopk., infestation advanced north and eastward from the 1971 infestation boundary in Yellowstone National Park. Infested trees were found in Indian Creek Campground at the north end of the park and around the north end of Yellowstone Lake. A ground survey showed an average of 15.5 infested trees per acre. A decrease in number of infested trees occurred in older infestation centers in the southwest corner of the park. The infestation will continue at epidemic status in areas containing susceptible stands.