Neurophysiological investigations – including sensory-evoked responses, contingent negative variation (CNV), and nerve conduction velocities – were done in 11 male polygonosomic patients and in comparison with a control group. Some significant data are reported pointing out differences which may be related to a hypovigil type (47, XYY) and a hypervigil type (47, XXY). The importance of the CNV and conduction velocity as an index of a constitutional minimal brain dysfunction is discus