The Mantel-Haenszel procedure (MH) is a practical, inexpensive, and powerful way to detect test items that function differently in two groups of examinees. MH is a natural outgrowth of previously suggested chi square methods, and it is also related to methods based on item response theory. The study of items that function differently for two groups of examinees, originally called item bias research, focuses on the fact that different groups of examinees may react differently to the same test question. The preferred, more neutral, term is differential item functioning (DIF). In studying DIF, members of the focal group and the reference group should be comparable. The item data may be arranged into 2 x 2 tables. Chi square procedures test a hypothesis, but do not produce a parametric measure of the amount of DIF exhibited by the studied item. The MH chi square test provides a measure of the size of the departure of the data from the null hypothesis. The data are presented in 2 x 2 tables, and the measure of DIF is in the scale of differences in item difficulty as measured in Educational Testing Services delta scale. MH is significantly less expensive to use than item response analyses. (GDC)