The relationship of cerebral neurotransmitters acetylcholine (ACh), noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5HT) to the energy state of the brain was examined in mice at various times following complete ischemia produced by decapitation, in gerbils submitted to transient global ischemia (10 min bilateral carotid artery occlusion, 5 or 30 min recirculation), and in rats 24 hr after irreversible microembolism. Ischemia caused significant reductions in brain monoamine concentrations. The alterations in NA, DA, and 5HT levels persisted during recirculation and were unrelated to energy restoration. They were accompanied by an increase in the concentrations of related metabolites, suggesting that synthesis was unable to compensate for the release of the transmitters at early post-ischemic time periods. As described for the catecholamines and 5HT, ischemia resulted in a significant decrease in ACh level, but recirculation was associated with a rapid increase in ACh concentration. Impaired synthesis and/or increased release of ACh can be responsible for the decrease in ACh concentration during ischemia. Early post-ischemic elevation of ACh may be related to the large increase in brain choline brought about by ischemia.