Abstract Both Nectria galligena and Ceratocystis fimbriata produced cankers on quaking aspen when inoculated with either spores or mycelium. In the first year canker development was more rapid in those trees inoculated with C. fimbriata than in those inoculated with N. galligena . After two years cankers caused by C. fimbriata usually did not enlarge further while those caused by N. galligena did. C. fimbriata did not cause cankers on red maple, or balsam poplar and only one canker on paper birch, while N. galligena produced cankers on all these hosts. Some kind of wound was necessary for successful infection by either fungus.