Regional cerebral blood flow (CBF) was measured by positron emission tomography (PET) with 15O-labeled water in an asphyxiated infant during a seizure. After intrauterine asphyxia, the infant had a syndrome characteristic of hypoxic-ischemic encephalopathy. During a PET scan on the second postnatal day, the infant had a focal seizure with deviation of eyes to the right and clonic jerking of the right arm. Regional blood flow was highest, about 80 m1/100 g/min, in the left temporal-parietal-frontal region of the left hemisphere, the site of origin of the seizure; blood flow in the same region on the other side was about 57 m1/100 g/min. These observations extend to the newborn previous demonstrations in older patients of a focal increase of CBF at the cerebral site of origin of a focal seizure.