The recent revival of interest in the potential of preventive medicine, reflected in its re-emergence as a medical specialism and in monitoring and campaigning activity at the local level, has been accompanied by growing interest in the history of public health. In particular, the work of the Medical Officers of Health (MOsH), the doctors appointed by many local authorities after 1850, has come under closer scrutiny. However, whereas historians have acknowledged that the MOsH played a key role in tackling environmental health and infectious disease in the second half of the nineteenth century, judgements have been less favourable for the period since 1900. It is alleged that the MOsH produced repetitive and complacent reports, delayed the introduction of immunization, and were seduced away from public health by hospital administration. Both they and their counterparts in the School Medical Service ignored wider threats to health such as malnutrition and unemployment, and campaigning on these issues was left to other individuals and pressure groups. Furthermore, it is argued that after the establishment of the National Health Service in 1948, MOsH failed to exploit the potential of health education, lagged behind thinking on social work, and were slow to develop services for 'community care'. According to this analysis, the demise of the MOH in the 1974 health service reorganization represented the logical culmination of trends in the previous 75 years. This paper examines the strengths and weaknesses of this interpretation, partly through a case-study based on the Midlands city of Leicester. It argues that, although some MOsH were complacent, all operated within the limitations of important local and national constraints, and that, given these restrictions on their room for manoeuvre, many were remarkably innovative and imaginative. The paper concludes that, until further research is undertaken, the charges levelled against these doctors remain largely unproven.