The relationship of the mean transit time of the vascular indicator C15O-labeled hemoglobin (tco) and the cerebral blood volume (CBV) as measured by stimulated x-ray fluorescence, to the mean arterial blood pressure (MABP) was examined in rhesus monkeys before and during experiment cerebral seizures. The results demonstrate a marked increase in CBV and a decrease in tco. A substantial portion of these changes is the passive accompaniment of the associated increase in MABP.