It has become commonplace in accounts of medicine in the second half of the twentieth-century to ascribe an “antibiotic revolution” to the years when penicillin became widely available from the early 1950s. However, to date there have been hardly any studies that demonstrate a major discontinuity in medical practices after mid-century, let alone that go on to specify their character. There would seem to be two key features of any “antibiotic revolution”: first and foremost that the treatment of diseases was transformed as doctors were able to cure illness caused by infections with specific drugs that eliminated causative bacteria; and second that the ambition of doctors to intervene with drugs in a number of diseases grew, as did the ability of the pharmaceutical industry to supply an increasing range of targeted and effective remedies. In this article we contribute towards an assessment of the first of these key features by discussing the changing management of acute bronchitis from the mid-1940s to the early 1960s. The disease was amongst the most prevalent and important of that period in Britain, being the single largest cause of consultations with general practitioners (GPs) through much of the 1950s. Bronchitis was also the subject of many high profile debates among doctors and health care agencies as concerns about its morbidity and mortality touched on such issues as smoke pollution, the costs of the National Health Service (NHS) and changes in the doctor–patient relationship. The evidence of contemporary studies shows that the treatment of acute bronchitis changed radically after the introduction of antibiotics, such that by the mid-1950s over 80 per cent of patients diagnosed with the condition were prescribed penicillin or another antibacterial drug—a shift that was not supported by any clinical trials or systematic evidence. How and why this change occurred are the questions we set out to answer.