There is nothing new about supervision in primary health care service delivery. Supervision was even conducted by the Egyptian pyramid builders. Those supervising have often favoured ridicule and discipline to push individuals and communities to perform their duties. A traditional form of supervision, based on a top-down colonial model, was originally attempted as a tool to improve health service staff performance. This has recently been replaced by a more liberal "supportive supervision". While it is undoubtedly an improvement on the traditional model, we believe that even this version will not succeed to any great extent until there is a better understanding of the human interactions involved in supervision. Tremendous cultural differences exist over the globe regarding the acceptability of this form of management. While it is clear that health services in many countries have benefited from supervision of one sort or another, it is equally clear that in some countries, supervision is not carried out, or when carried out, is done inadequately. In some countries it may be culturally inappropriate, and may even be impossible to carry out supervision at all. We examine this issue with particular reference to immunization and other primary health care services in developing countries. Supported by field observations in Papua New Guinea, we conclude that supervision and its failure should be understood in a social and cultural context, being a far more complex activity than has so far been acknowledged. Social science-based research is needed to enable a third generation of culture-sensitive ideas to be developed that will improve staff performance in the field.