In the estimation of intellectual level the adherents of the Binet-Simon scales still claim for it a predominant position (1). This type of code is empirically constructed, and relies on obtaining small samples of cognitive behaviour of widely different kinds (2). There is, however, another system of testing, diametrically opposed in principle to the Binet plan. This, which is sometimes styled the factorial principle, acknowledges its theoretical dependence on the well-known conceptions on Intelligence of Prof. Spearman (3). The factorial tests are specifically designed to measure the statistically determined “general factor” only. Both methods have their advocates and the theoretical advantages and disadvantages have been hotly debated. The theoretical aspect is not of concern in the present study however. This was undertaken to discover whether the Cattell series of scales—perhaps the most important factorial test series (4)—could be used with advantage to replace or supplement the Binet scales, e.g. the widely used Terman-Merrill Revision—in the clinical examination of adult defectives, who are mainly of high grade. The scales have been compared, in other words, from the point of view of clinical practice, rather than of scientific theory.