Recent guidelines from the US National Institutes of Health (NIH) mandate the inclusion of adequate numbers of women in clinical trials. Ought such standards to apply internationally? Walzer's theory of justice is brought to bear on the problem, the first use of the theory in research ethics, and it argues for broad application of the principle of adequate representation. A number of practical conclusions for research ethics committees (RECs) are outlined. Eligibility criteria in clinical trials ought to be justified by trial designers. Research ethics committees ought to question criteria that seem to exclude unnecessarily women from research participation. The issue of adequate representation should be construed broadly, so as to include consideration of the representation of the elderly, persons with HIV, mental illness and substance abuse disorders in clinical research.