A judicious combination of qualitative and quantitative methods can play a valuable role in health services research. This paper reviews the main reasons for combining methods: for different stages in a project; to compensate for the shortcomings of individual methods; and for the purpose of 'triangulation'. It examines the potential for qualitative approaches to contribute to quantitative work--by providing insights into the process of data construction, identifying relevant variables to be studied, furnishing explanations for unexpected or anomalous findings, and generating hypotheses or research questions for further investigation. Similarly, qualitative work can be enhanced by using quantitative techniques--albeit often in a modified form--in analysing data, developing sampling strategies, and amalgamating findings from separate qualitative studies. Although there is potential to develop multi-method approaches, there remains an important role for rigorous studies employing either qualitative or quantitative methods.