Survival of 4 days old rats exposed to 6% O2-94% N2 was studied. Administration of L-DOPA (100 mg/kg) or L-5-HTP (100 mg/kg) reduced survival during hypoxia to about 30% of controls. A further reduction of survival time was noted after combined administration of L-DOPA and L-5-HTP. Administration of increasing doses of L-DOPA or L-5-HTP resulted in a dose-related decrease in neonatal survival time. After inhibition of the peripheral L-aminoacid decarboxylase with MK-486, L-DOPA caused the same reduction of survival time during hypoxia as after L-DOPA alone. Clonidine (2 mg/kg) was found to reduce hypoxic survival time to about 60%, while apomorphine had no effect compared to controls. Clonidine and apomorphine together had the same effect as clonidine alone. It is suggested that central monoamine neurotransmitters are involved in the mechanisms determining survival during neonatal oxygen deprivation.