Animals exposed to 6% oxygen showed a partial inhibition of the rate of tyrosine hydroxylation and a blockade of the conditioned avoidance response. The behavioral disruption was suggested to result, at least in part, from a dopaminergic disturbance, since the behavior was restored by the administration of DOPA or apomorphine but not by 5-hydroxytryptophan. Biochemical data showed a selective retardation in brain dopamine (DA) disappearance after synthesis inhibition. Methoxytyramine formation was markedly retarded. Analysis of this effect indicated that the decreased DA turnover was related to the release of transmitter rather than to an effect on catechol-O-methyltransferase (COMT) or monoamine oxidase (MAO). In addition, there was evidence for a partial inhibition of MAO activity by hypoxia as well as a decreased activity of dopamine-betahydroxylase. It was concluded that the disruption of behavior was related to decreased dopaminergic receptor activation and that decreased synthesis played at most a contributory role.