Credible and useful methodologic evaluations are essential for increasing the uptake of effective cancer screening tests. In the current article, the authors discuss selected issues that are related to conducting behavior change interventions in cancer screening research and that may assist researchers in better designing future evaluations to increase the credibility and usefulness of such interventions. Selection and measurement of the primary outcome variable (i.e., cancer screening behavior) are discussed in detail. The report also addresses other aspects of study design and execution, including alternatives to the randomized controlled trial, indicators of study quality, and external validity. The authors conclude that the uptake of screening should be the main outcome when evaluating cancer screening strategies; that researchers should agree on definitions and measures of cancer screening behaviors and assess the reliability and validity of these definitions and measures in different populations and settings; and that the development of methods for increasing the external validity of randomized designs and reducing bias in nonrandomized studies is needed. Cancer 2004. © 2004 American Cancer Society.