Two groups of male Sprague-Dawley rats received from weaning 50 micrograms/ml of mercury as mercuric chloride (HgCl2) in drinking water for 320 and 350 days. Hg exposure increased cardiac inotropism, without chronotropic changes, in both groups, and induced arterial hypertension in the rats exposed for 350 days. In the exposed rats, cardiovascular responses to the stimulation of peripheral alpha and beta adrenoceptors were decreased and increased, respectively, possibly through a reduced intracellular availability of calcium ions for contractile mechanisms. Hg exposure did not affect either vagal or sympathetic activity or cardiovascular reactivity to several physiological agonists. On the other hand, Hg exposure induced baroreflex hyposensitivity and produced a drastic alteration of the levels of copper and zinc in brain and kidney.