The effect of acute and chronic cadmium (Cd) administration on the vascular function of the rat aorta was studied. The rats were randomly divided into four main groups (A: saline controls under chronic administration, B: Cd-treated rats under chronic administration, C: saline controls under acute administration, D: Cd-treated rats under acute administration). After their sacrifice, the aortic rings were divided into rings with endothelium (E+) and without (E-), and suspended in an isolated organ bath with Krebs - Henseleit buffer. Maximal tension (T max, in g) was measured in response to potassium chloride (KCl) and phenylephrine (PE) in all aortic rings. Relaxation response to acetylcholine (ACh) administration was expressed as percent of maximal tension induced by PE. Chronic administration: A statistically significant increase of the contraction was observed between groups B (i.m. Cd 0.5 mg/kg for 120 days) and A (i.m. 0.9% NaCl for 120 days) in response to KCl (20-60 mM) and the T max as well (in both the E+ and the E- subgroups). No statistically significant difference was observed in response to PE and ACh exposure. Acute administration: A statistically significant increase was observed between group D(E+) (i.m. Cd 2 mg/kg, 8 h before sacrifice) and group C(E+) (i.m. 0.9% NaCl, 8 h before sacrifice) in response to 10-30 mM of KCl, and a significant decrease between D(E-) and C(E-) in response to 10(-7)-10(-6) M of PE, though T (max) was increased between D(E-) and C(E-) with PE exposure. The contractile response levels of the E+ aortic rings to PE and ACh showed no statistically significant difference.