1. Stimulation of the mesolimbic dopamine system, by micro-injection of the substance P analogue [pGlu5,MePhe8,Sar9] substance P (DiMe-C7) into the ventral tegmental area induced a prolonged increase in blood pressure and circulating levels of vasopressin. 2. In the present study, this treatment produced a significant decrease of cardiac baroreflex sensitivity in conscious rats. After pretreatment with the dopamine receptor antagonist raclopride, central stimulation failed to produce any changes in baroreflex parameters. 3. The central dopamine-mediated decrease in baroreflex sensitivity may be involved in functionally potentiating the circulatory actions of vasopressin.