This article provides a comparative analysis of adversarial framing oriented to reputation discrediting in the context of social movement/counter-movement relations. Website material associated with two Canadian organizations, the Natural Resources Stewardship Project (NRSP) and DeSmogBlog (DSB), involved on opposite sides of the contention over anthropogenic global warming (AGW), is analysed to examine how each side identifies and frames its adversaries and the latter's claims-making practices. The analysis focuses on the extent to which the structure of adversarial framing by each side differs from or is mirrored by the framing of the other side. Both sides discredit their opponents on the basis of five reputational dimensions: practices, moral character, competence and qualifications, social associations, and real versus apparent motivations. The principal point of difference concerns the main focus of discrediting, with the NRSP focusing chiefly on its opponents' claims-making practices and the DSB on moral character. Both discourses, nonetheless, create an integrated discrediting narrative in which all five dimensions are involved, with motivation acting as a cognitive and normative thread tying the other dimensions together.