Behavioral and neurochemical results refer to an impairment of the dopaminergic system produced by hypoxia. The chemically (K+, amphetamine) and electrically stimulated release of dopamine from rat striatum slices which were preloaded with labeled dopamine following exposure to hypobaric hypoxia was determined. The effect of hypoxia consists in a marked inhibition of dopamine release depending both on the degree of hypoxia and on the kind of stimuli used. Dopamine release inhibition reflects not only the direct effect of hypoxia, which seems connected especially with the vesicular compartment, but also adaption and restitution processes. Regarding the effects on rats at the age of 2 wk, the resistance of young animals against hypoxia may be founded upon missing vesicular mechanisms of distinct vulnerability.