The circulating renin–angiotensin system (RAS) is well known for its systemic role in the regulation of blood pressure, renal hemodynamics and fluid homeostasis. However, in mammals several organs also contain a local RAS, including male and female reproductive tissues. In the present study we analysed serum from a free-living population of red deer (Cervus elaphus hispanicus) and fallow deer (Dama dama) to determine the activity of four RAS-regulating aminopeptidases (aminopeptidase A, aspartyl aminopeptidase, aminopeptidase N and aminopeptidase B) as part of a study of annual cycles of growth and condition. Our aim was to detect seasonal variations in the activities of these aminopeptidases and their relationship to the reproductive behaviour of both species in a Mediterranean environment. In both males and females there was a maximum peak of activity in autumn. A second peak was detected in spring for males while in females activity was also higher in summer. These changes may be related to a different endocrine status according to their seasonal cycle, the decreased photoperiod in autumn and the normal timing of the seasonal growth cycle. Thus, changes in the activity of RAS-regulating aminopeptidases could reflect the functional role of angiotensins through the annual cycle of both species, also suggesting an important role of these peptide hormones in the regulation of these biological processes.