Field tests were made of the fungal inoculation method of Reid et al. which assesses the potential of individual lodgepole pine trees (Pinus contorta Dougl var. latifolia Engelm.) to resist attacks by mountain pine beetle (Dendroctonus ponderosae Hopk.). Four hundred and eighty-four trees were inoculated with one of the beetle’s mutualistic blue-staining fungi (Europhium clavigerum Robinson and Davidson), tree responses were determined, and the potential of each tree to resist D. ponderosae was predicted. Two months later, after mountain pine beetles had attacked some of these same trees, most of the predictions based on the fungal assay system proved to be incorrect. Most of the trees which were attacked and which had been rated potentially resistant did not prevent successful bark beetle reproduction. These results, contrary to those of Shrimpton and Reid, suggest that some improvement is needed in the fungal assay method of assessing resistance of lodgepole pine to mountain pine beetle. Measures of tree resistance based on success of mountain pine beetle reproduction showed no difference in the proportion of non-resistant trees between epidemic and endemic areas.