Meta-analysis is an important technique for synthesizing research findings. Although the statistical foundations of meta-analysis continue to be debated, few question its value as a rigorous framework for organizing literature reviews. In recent years, there has been increasing emphasis on the use of meta-analysis not only to summarize the central tendency of findings but also to explain variation between studies. This article reviews the major steps in a meta-analysis with an emphasis on comparative analysis of subgroups of studies. A meta-analysis of the antihypertensive efficacy of calcium channel blockers is used to illustrate how a comparative analysis can be applied to investigate racial variation in the effects of calcium channel blockers. A statistically significant trend is found between the proportion of African-American hypertensive subjects and the mean reduction in blood pressure. Meta-analytic techniques also are applied to explore possible confounders due to differences in research design and patient characteristics.