a total of 241 isolation attempts were made, with 233 yielding cultures from 61 branches collected from two balsam fir trees. the most commonly found fungal endophyte in healthy branches of balsam fir was foveostroma abietinum, followed by geniculosporium sp. and zythiostroma pinastri, while in witches’ broom twigs the most common fungal endophyte was phoma sp. 1, followed by foveostroma abietinum, and thelebolus caninus. a modification of good’s hypothesis was used to calculate the percentage of total biodiversity likely to be found in the surveyed twigs, and the values of 46.6% and 55.6% were obtained for healthy twigs and witches’ broom twigs respectively. approximately half of the fungal endophyte diversity is represented in this study according to the modification of good’s hypothesis, however, further research should be conducted to further understand the fungal endophyte diversity in both healthy and witches’ broom twigs.