To investigate the possible correlation between changes in monoaminergic neuronal activity and cerebral blood flow (CBF) in the same brain regions after subarachnoid hemorrhage (SAH), monoamine levels were analyzed by both HPLC-ECD and fluorohistochemistry techniques, and CBF was measured by using colored microspheres. At the second day of SAH, significant and nonsignificant reductions in blood flow were seen in the examined brain regions with a marked increase in CBF appearing in the telencephalon and hypothalamus on the third day, Significant reductions of monoamine levels in most brain regions were also observed on the second day after SAH, whereas norepinephrine (NE) levels in midbrain increased to 1.5 times compared to the normal level. These reductions were sustained until the fourth day of SAH, although at the third day, serotonin (5-HT) and dopamine levels in the hippocampus and 5-HT levels in the cerebellum were significantly elevated. In fluorohistochemical studies, the fluoro-intensities of monoamines, particularly catecholamines, in the midbrain dorsal NE bundle were enhanced at the second day after SAH. These NE neurons originated from the A6 cell group close to the area where homologous blood was applied through the cisterna magna. The results obtained after SAH show an apparent correlation between changes in monoamine levels and CBF in norepinephrine (NE)-rich areas. These results suggest that SAH-induced neuronal dysfunctions, particularly with NE neurons, are caused not only by reductions of blood flow but also by hemorrhage. (C) Elsevier Science Inc.