In an effort to determine to what extent cerebral blood flow (CBF) varies in different parts of the brain after prolonged fetal hypoxia, we measured flow to 34 regions. In seven chronically catheterized fetal lambs at 130 to 140 days' gestation, flow was measured by means of radioactive labeled microspheres during a control period, during hypoxia, and at 4, 24, and 48 hours after hypoxia. Control blood flow to cortical, subcortical, and brain stem structures respectively equaled 221, 237 and 275 ml . min-1 . 100 gm-1. After 90 minutes of hypoxia, flows respectively increased 67%, 93%, and 160% to these areas, suggesting preferential shunting of flow to critical brain stem regions. By 4, 24, and 48 hours after hypoxia the regional flows ahd returned to values not significantly different from control values. We conclude that: (1) significant fetal regional cerebral blood flow differences occurred in utero, with brain stem and subcortical flows being greater than flows to other regions of the brain; (2) during prolonged intrauterine hypoxia, total cerebral blood flow increased about 95%, with evidence of preferential shunting to critical brain stem regions; (3) during the posthypoxic recovery period at 4, 24, and 48 hours, flows returned to normal, indicating no evidence of a post-ischemic hypoperfusion syndrome or impairment of the microcirculation.