A comatose 31-year-old male with presumed viral encephalitis and frequent partial motor seizures was paralyzed with pancuronium in an attempt to reduce recurrent elevation of intracranial pressure (ICP) associated with each seizure. ICP was continuously monitored with a Richmond Bolt and 5 electrographic seizures originating in the left frontal area were recorded. Each ictal episode was associated with stable blood pressure and an increase of ICP. The average seizure duration was 78 +/- 17 sec (mean +/- S.D.) and the average maximum increase of ICP above baseline during the seizures was 6.5 +/- 0.6 mm Hg with average peak ICP of 16.0 +/- 0.86 mm Hg. A simple mathematical model predicts the rate of increase of ICP, the peak ICP, the phase difference between maximum spike frequency and maximum ICP, and the rate at which ICP returns to pre-ictal values after termination of the seizure. The predicted values of ICP closely approximate the experimentally derived data. Therefore, the time course of the ICP appears to be determined by the frequency of the fundamental units of abnormal synchronized activity (the epileptogenic spike) and the CSF pressure-volume dynamics existing at the time of the seizure. An average increment of ICP per spike can be calculated for each seizure. The model also predicts that patients may develop high ICPs due to prolonged seizures. Prolonged unrecognized seizures may occur in patients who are therapeutically paralyzed as demonstrated by the case described here.