The cerebrovascular response to submergence asphyxia was studied in the Pekin duck (Anas platyrhynchos var.) by use of the cerebral blood flow (CBF) tracer [14C]isopropyliodoamphetamine and quantitative autoradiography. Blood flow of the whole brain was 158 +/- 14 (SE) ml.min-1 x 100 g-1 (n = 7) in control animals. There was a doubling of flow to 320 +/- 61 ml.min-1 x 100 g-1 (n = 6) during submergence asphyxia. The hypothesis that CBF is redistributed within the brain during asphyxia was not supported. There were no regional reductions in CBF during submergence asphyxia. Mean arterial blood pressure was similar (approximately 140 mmHg), but heart rate, arterial blood gas tensions, and arterial pH were significantly different in control and submerged ducks at the time CBF was measured. The differences in CBF among submerged animals correlated strongly with arterial PCO2 and mean arterial blood pressure. The smallest proportional difference in regional CBF between control and submerged ducks occurred in the ectostriatum (+141%) and the largest in the locus ceruleus (+241%). The largest absolute difference in regional CBF was in the nucleus ruber (+322 ml.min-1 x 100 g-1). These are the first measurements of blood flow in discrete nuclei and regions of the avian brain.