In a group of 15 patients with chronic unilateral cerebral ischemia, a quantitative EEG study was performed before, during and after nimodipine (Bay e 9736) infusion (1 microgram/kg/min). The EEG was recorded bipolarly from the rolandic region. After computerized EEG analysis, a multiparametric asymmetry score (MAS) was calculated; this MAS provides a sensitive indicator for discrimination between neurologically normal subjects and patients with unilateral ischemia. A positive MAS is characteristic for healthy subjects, a negative one for ischemia patients. During nimodipine treatment, the MAS became more negative (increased EEG asymmetry) in 7 and less negative (decreased EEG asymmetry) in 8 patients. A correlation was found between the direction of the EEG asymmetry changes and the localization of the infarcted area as seen in the CT scan.