Examples of cross-cultural stability or instability of mental test items are illustrated. A statistical procedure involving the cross-plotting of item difficulties for two different groups and generating a line of mutual regression through the resulting scatter of points is described. D-values, representing the perpendicular distance, in delta units, from the line of mutual regression, for all items in a given subtest (in this case, mathematics) are presented in a computer generated table for the following groups studied: American Indian, Afro-American, Mexican-American, Puerto Rican, other Latin-American, Oriental-American, White Eastern, White Southern, and White Western. (Author/RC)