Within the emerging paradigm of experimental Critical Discourse Analysis, this paper investigates the framing effects of dehumanising vs militarising metaphors in anti-immigration discourses. These metaphors are characterised as 'extreme metaphors' in so far as they are manifestly metaphorical and obviously inflammatory. Attested examples of these metaphors in political and media discourses are identified and critically analysed before their potential framing effects are investigated experimentally. Contrary to predictions, alternative metaphors did not increase support for actions and evaluations consistent with the unique framings that they present. In fact, extreme metaphors decreased support for anti-immigration sentiments and hostile immigration policies compared to literal framings. It seems that extreme metaphors alert readers to the metaphorical framing being presented so that, among certain groups of people, the framing is more readily scrutinised and rejected, prompting readers adopt more sympathetic attitudes toward immigration. The implications of these findings for Critical Discourse Analysis are discussed.