The purpose of this investigation was to assess the intellectual function of patients on regular dialysis treatment by using neuropsychological tests such as the Wechsler Adult Intelligence Scale (WAIS) and the Wechsler Memory Scale (WMS). Studies were performed on 54 patients; 21 patients were retested after at least 12 months. We found no relationship between the neuropsychological scores and the blood levels of small molecules, the hemoglobin concentrations, the serum aluminium levels, and the levels of formal education. We found, however, an impairment of neuropsychological performance, mainly for memory function, related to the duration of dialysis and, possibly, to parathormone levels. We conclude that standard hemodialysis strategies are not able to prevent the development of intellectual impairment in uremic patients and that the WMS could be used as a sensitive objective measure of the comparative adequacy of various long-term dialysis treatments.