The subject of this investigation is the study of the immediate mental changes after standard leucotomy up to a time when the more acute manifestations of the brain operation have subsided and a stage of stabilization has been reached. Altogether twenty cases were examined, most of them schizophrenics. The observation time was between eight weeks and twelve months. The patients were examined in the first eight to ten days every day, and later at longer intervals according to their stabilization. In about half of the cases a detailed assessment of the patient's personality and intellectual faculties with a battery of tests was made before the operation. An assessment was also made of the patients' special abilities and knowledge, their general outlook and interests that had not been covered by the routine testing. The aim of the investigations was first to obtain a detailed picture of the acute condition following the operation, generally referred to as a confusional state, and to follow up the reorganization of these defects. Our next objective was to find out what significance these initial changes, or particular components of them, might have on the final result of the operation.