In the current study, we aimed to describe changes in plasma MMP-2 and MMP-9 activities in the most-used experimental model of essential hypertension—spontaneously hypertensive rats (SHR), depending on the age of the experimental animals (7-, 20- and 52-week-old ones: SHR-7, SHR-20, and SHR-52) and their normative control of Wistar-Kyoto rats (WKY: WKY-7, WKY-20, and WKY-52). The gene discussed is MMP9; the disease is essential hypertension.