Extensive preoperative and postoperative psychological examination was carried out in every case where bilateral prefrontal lobotomy was performed as a therapeutic resort. In addition to recording detailed clinical notes, each patient was subjected to a variety of standardized psychological testing procedures designed to sample behavior at various levels of complexity. The tests used were: a modified form of the Kohs Block Design; a modification of the Weigl-Scheerer-Goldstein Color-form Sorting Test; a test of grouping behavior patterned after that suggested by the work of Vigotsky and Halstead; and a modified use of the Rorschach Test. An analysis of the results of the preoperative and postoperative adm. of these tests shows that all patients do not exhibit impairment or deterioration of abstract thinking following prefrontal lobotomy. In the series of cases presented, the 2 patients who did not show preoperative impairment of these functions also failed to show impairment in the postoperative period. On the basis of the cases studied there is question as to whether the impairment in abstract behavior noted following lobotomy is a function of surgical insult to the intact brain or whether it is a residual of the preoperative psychotic structure. The author states that it is clear from the data collected "that clinical improvement may occur in the absence of improvement in abstract behavior and, conversely, there may be decided improvement in abstract functions without noticeable improvement in the general behavior patterns of the patient.".