Randomized controlled trials (RCTs) have an important place in the assessment of the efficacy of complementary and alternative medicine (CAM). However, they address only one, limited, question, namely whether an intervention has-statistically-an effect. They do not address why the intervention works, how participants are experiencing the intervention, and/or how they give meaning to these experiences. Therefore, we argue that the addition of qualitative research methods to RCTs can greatly enhance understanding of CAM interventions. Qualitative research can assist in understanding the meaning of an intervention to patients as well as patients' beliefs about the treatment and expectations of the outcome. Qualitative research also assists in understanding the impact of the context and the process of the intervention. Finally, qualitative research is helpful in developing appropriate outcome measures for CAM interventions. Greater understanding of CAM interventions has the potential to improve health care delivery.