Mountain pine beetle infestations in second-growth ponderosa pine have been chronic in the Little Belt and Big Snowy Mountains since 1947. In 1976, increasing numbers of attacked trees were observed. Current infestation intensity averages 82 trees per hectare. Losses are expected to continue as long as stands remain stagnates. Commercial sales and thinning to reduce basal area below 34 m /ha* are recommended. Precautions are given to prevent population buildup of secondary bark beetles.