The Wechsler Adult Intelligence Scale and the Wechsler Memory Scale were administered to 32 patients both before and six months after they received open prefrontal leucotomies. The preoperative and postoperative test results are compared, consideration being given to individual patients as well as to the group. The mean results for the group provide no evidence of any post-operative intellectual deterioration. However, it seems probable that in individual cases such deterioration occurred. In most of these cases brain damage would appear to be responsible, and the ability "to comprehend and size up a total situation" is seen as the area of functioning primarily affected.