Quantitative measures of area of sway, total sway, and cognitive function failed to show significant differences in acute (50 minute) "ON-OFF-ON-OFF" studies of high frequency left vagal stimulation in three epileptic patients undergoing treatment for chronic complex partial seizures. Fluctuation in blood levels of anticonvulsants may have been associated with some clinical effects. There were no significant adverse effects of acute left vagal stimulation in these three subjects.