While increasing attention is being paid to the feasibility of incorporating quality of life investigations into cancer clinical trials, and QOL data have played a prominent role in some recent trials, such studies remain the exception rather than the rule. This paper addresses a number of measurement, research design, and implementation issues surrounding clinical-trial-based quality of life studies. These include: the appropriate source of quality of life data; global versus multidimensional approaches to conceptualizing quality of life; the feasibility and desirability of a quality of life measurement "gold standard;" generic versus disease-specific measures; the role of psychometrics in selecting quality of life measures; the frequency and timing of data collection; and patient accrual and differential loss to follow-up. Where appropriate, areas of real or potential consensus on the methods of conducting quality of life investigations are highlighted.