While the release of neurotransmitters is involved in the pathophysiology of brain damage following birth asphyxia, it also plays a role in endogenous defense against such damage. Levels of monoamines and the main cerebral monoamine metabolites in the cerebrospinal fluid (CSF) were measured in asphyxiated and control infants within 24 h after birth. The results indicate an increased turnover of noradrenaline (NA) and dopamine following asphyxia. Furthermore, the NA stores in the brain seem to be exhausted in some cases. We conclude that this increase in catecholamine turnover to some extent explains the clinical symptoms of hypoxic-ischemic encephalopathy and that it may reflect an intrinsic adaptive capacity to perinatal distress.