- The importance of measuring changes in a patient's quality of life when evaluating the efficacy of new drugs is increasingly recognised. In this paper, we review the steps associated with this process--recognising the opportunity and the need to include quality of life instruments during the investigation, choosing the most suitable instrument(s) and interpreting the results. To be useful in clinical trials, quality of life measures must be both responsive (able to detect all important differences) and valid. Generic instruments are applicable to a wide variety of populations but may lack responsiveness. Disease-specific instruments are more likely to be responsive and are directly relevant to patients and clinicians. The approach to measurement in a specific clinical trial should be dictated by the goals of the investigators.