The aim of this study was to investigate the EEG power spectra obtained during rest and mental processing in chronic stroke patients. Seventeen patients with stabilized unilateral cerebral ischemia, grouped according to the side of lesion, underwent quantitative EEG recordings during rest and attentive/cognitive tasks. EEG spectral values were compared with those of 11 healthy subjects. Patients displayed different EEG patterns from controls, under rest condition: patients with left hemispheric lesion were characterized by a preserved alpha and beta band "reactivity," with a lack of significant changes in slow band components. In patients with right hemisphere lesion, no significant changes of the slow and fast band activities were evident during each task. These findings indicate that different EEG patterns of activation characterize stroke patients with left and right hemispheric damage.