ABSTRACT Many people argue that disagreements and inconsistencies between Research Ethics Committees are morally problematic and there has been much effort to ‘harmonise’ their judgements. Some inconsistencies are bad because they are due to irrationality, or carelessness, or the operation of conflicting interests, and so should be reduced or removed. Other inconsistencies, we argue, are not bad and should be left or even encouraged. In this paper we examine three arguments to reject the view that we should strive for complete (...) consistency between committees. The first argument is that differences in judgement are not necessarily incompatible with ideas of justice for patients who are potential participants of research reviewed by different committees. We call this ‘the justice argument.’ The second argument is that such committees do not have access to a single moral truth, to which their judgement is supposed to correspond. We call this the ‘moral pluralism argument.’ The third argument is that the process of ethics committee review is also morally relevant and not solely the outcome. We call this the ‘due process argument.’ While we fall short of establishing exactly how much variation and on what substantive issues would be ethically permissible, we show that it is largely inevitable and that a certain amount of variation could be seen as a desirable part of the institution of medical research. (shrink)