In the present report the results are discussed of a psychological testing program which was apart of the preparation for a multi-disciplinary, national investigation into the need for guidance of the mentally de ficient. A team of sociologists traced two groups of children, ten and thirteen years old respectively, and suspected of mental deficiency. The psychologists subsequently tested this sampie in order to decide whether the subjects could indeed be regarded as mentally deficient, if an intelligence quotient of 79 or lower is taken as criterion. As a second assessment task, a systematic categorization with a view to the expected needs for guidance was attempted. For this purpose the total sampie was divided into subgroups on the basis of test result patterns. RESEARCH QUESTIONS The analysis of the data from this sampie provided an interesting op portunity for a number of explorations into both theoretical and prac tical questions, which are only partly related to the aims of the investi gation. These questions concern the merits of the tests used, the structure of the test scores in the sampie under investigation, and some other general problems about the sampie and the subpopulation of the mentally deficient. Questions about the tests concern their suitability for the investiga tion of mentally retarded subjects, in particular for assessing their need for guidance. Another question involves in which way the testing pro gram can best be reduced when for some children the time available is not sufficient for a complete administration.