Medical specialists play a pivotal role in health innovation evaluation and policy making. Their influence derives not only from their expertise, but also from their social status and the power of their professional organisations. Little is known, however, about how medical specialists determine what makes a health innovation desirable and why. Our qualitative study investigated the views of 28 medical specialists and experts from Quebec and Ontario (Canada) on three controversial innovations: electroconvulsive therapy, prostate-specific antigen screening and prenatal screening for Down's syndrome. Our findings indicate that the scientific, clinical and social arguments of medical specialists combine to create a relatively consistent narrative for each innovation. Our comparative analysis suggests that these narratives bring about a 'soft' resolution to controversies, which relies on a more or less tacit understanding of the social desirability of innovations and which sets the stage for their routinisation. Such an unpacking of medical specialists' arguments both for and against new technologies is needed because such arguments may easily be considered authoritative and because there are few forums for debating the social desirability of innovations not generally deemed to be highly controversial.