Abstract: Push-pull superfusion technique was used to investigate the release of endogenousgamma一aminobutyric acid(GABA)in the posterior hypothalamus of the conscious , freely moving ratin response to peripherally applied drugs or experimentally induced blood pressure changes. The rise in blood pressure elicited by intravenous infusion of phenylephrine(15μg·kg^-1·min^-1) or blood(3 ml/100g)was associated with an increased rate of GABA release in the posterior hypothalamus,Hypotension preduced by nitroprusside(30μg· kg^-1· min^-1) ,chlorisondamine(3mg·kg^-1,iv)and controlled bleeding(3ml/100g)led to a counteracting decrease in hypothalamic GABA outflow.This finding suggests that GABAergic neurons of the conscious,freely moving rat in the posterior hypothalamus are involved in cardiovascular control and possess a hypotensive function.