Previous studies have shown that aluminum (Al) could inhibit parathyroid function. However, controversy still remains about the possible mechanisms implicated. Thus, the aim of this study was to evaluate the acute parathyroid hormone (PTH) response to intravenous Al infusion. Male Wistar rats were divided into two groups: Group A (n = 5): received 0.1 ml of saline. Group B (n = 5): received 0.5 mg of Cl3Al in 0.1 ml of saline. In both groups ionized calcium (Ca(+)+) decreased, but despite a similar degree of haemodilution, this change was only significant in group A. This variable Ca(+)+ decrease was followed by different responses in the PTH secretion. In group B there was a significantly (p less than 0.05) lower PTH release compared with control group. These results suggest that Al could directly inhibit the PTH secretion, and at the same time might exert an indirect effect on PTH release "blunting" the serum Ca(+)+ variations.