The 19th century saw the development of an eclectic medical marketplace in both the United Kingdom and the United States, with mesmerists, herbalists and hydrotherapists amongst the plethora of medical ‘sectarians’ offering mainstream (or ‘allopathic’) medicine stiff competition. Foremost amongst these competitors were homoeopaths, a group of practitioners who followed Samuel Hahnemann (1982[1810]) in prescribing highly dilute doses of single-drug substances at infrequent intervals according to the ‘law of similars’ (like cures like). The theoretical sophistication of homoeopathy, compared to other (...) medical sectarian systems, alongside its institutional growth after the mid-19th-century cholera epidemics, led to homoeopathy presenting a challenge to allopathy that the latter could not ignore. Whilst the subsequent decline of homoeopathy at the beginning of the 20th century was the result of multiple factors, including developments within medical education, the Progressive movement, and wider socio-economic changes, this article focuses on allopathy’s response to homoeopathy’s conceptual challenge. Using the theoretical framework of Berger and Luckmann (1991[1966]) and taking a Tory historiographical approach (Fuller, 2002) to recover more fully 19th-century homoeopathic knowledge, this article demonstrates how increasingly sophisticated ‘nihilative’ strategies were ultimately successful in neutralising homoeopathy and that homoeopaths were defeated by allopaths (rather than disproven) at the conceptual level. In this process, the therapeutic use of ‘nosodes’ (live disease products) and the language of bacteriology were pivotal. For their part, homoeopaths failed to mount a counter-attack against allopaths with an explanatory framework available to them. (shrink)