Hyperventilation evoked abnormal EEG discharges or discharges and clinical seizures in 11% our patients with partial complex seizures. Hyperventilation is useful in the diagnosis of this kind of epilepsy, but may need to be pursed more vigorously and for a longer duration than is usual practice. The vigorous use of hyperventilation in selected patients with partial seizures should be employed before the use of other more complicated, expensive, and potentially harmful activating procedures.