Magnetic resonance imaging (MRI) can now provide maps of human brain function with high spatial and temporal resolution. We aimed to establish whether this noninvasive technique could also map the cortical activation that occurs during focal seizures. In order to do this, we used a conventional 1.5-tesla clinical MRI system for the investigation of a 4-year-old boy suffering from frequent partial motor seizures of his right side. We acquired FLASH images (TE = 60 msec) every 10 seconds over intervals of 10 minutes and derived activation images by subtracting baseline images from images obtained during clinical seizures. Functional MRI revealed sequential activation associated with specific gyri within the left hemisphere with each of five consecutive clinical seizures, and also during a period that was not associated with a detectable clinical seizure. The activated regions included gyri that were structurally abnormal. We concluded that functional MRI can provide new insights into the dynamic events that occur in the epileptic brain and their relationship to brain structure.