In a preliminary investigation, an impairment index scale developed by one of us (W.C.H.) for reflecting impairment of biological intelligence has been applied to 8 carefully selected individuals before and after prefrontal lobotomy and to another individual following lobotomy. Several of these cases were found to exhibit an impairment of biological intelligence prior to lobotomy. This operation did not consistently alter the degree of impairment manifested quantitatively in contrast with high impairment scores obtained for frontal lobectomies. This would seem to point to the cortex of the frontal lobes as the region of the brain in which the functions reflected by the impairment index are maximally represented or localized.It is concluded that:1. Impaired biological intelligence, as encountered in some forms of psychopathy, is not relieved by the operation known as prefrontal lobotomy.2. Lobotomy may not increase the degree of impairment of this function. [See Fig. 2 In Source Pdf].3. Little is known concerning the behavioral effects of prefrontal lobotomy.