Aminopeptidases (APs) play a major role in the metabolism of circulating and local peptides, such as angiotensins and vasopressin, substances involved in the control of blood pressure and water balance. In the present work, we studied the influence of dehydration on angiotensinases and vasopressin-degrading activity. Since sex differences may exist in the regulation of water balance by angiotensin II and differential sexual steroid modulation of vasopressin secretion, in response to osmotic stimulation have been reported, gonadotropin releasing hormone (GnRH)-degrading activity was also analysed in serum, neurohypophysis and adrenal glands of male and female rats. Our results did not suggest sex differences in the response to changes in osmolality. GnRH-degrading activity decreased in serum of dehydrated males and females, which suggests a longer action of the peptide under these conditions. In neurohypophysis, there was an increase in the activity of aminopeptidase A (APA), the enzyme responsible for the metabolism of angiotensin II to angiotensin III. This occurs with a decrease in alanyl aminopeptidase activity, which would lead to a prolonged action of angiotensin III by reduction of its metabolism. In adrenals of dehydrated animals, the results would imply a high degree of metabolism of angiotensin III and vasopressin.