We have reviewed 4 international sets of guidelines for the economic evaluation of pharmaceutical products-those of the Australian Pharmaceutical Benefits Advisory Committee, the Canadian Coordinating Office for Health Technology Assessment, the Ontario Ministry of Health, and the England and Wales Department of Health. Comparison of these guidelines reveals that there are a number of differences between them, including disparities in outcome selection, costs and perspectives. These observations were attributed to differences in study purpose, conceptual approach, measurement techniques and value judgements. Uniformity can be achieved only in conceptual approach and measurement technique. Guidelines should be flexible to accommodate differences in the study purposes and value judgements of the analysts.