We analyze here the immunohistochemical expression of four crucial peptidases in RAS [neutral endopeptidase/CD10 (NEP/CD10), angiotensin-converting enzyme-2 (ACE2), aminopeptidase A (APA), and angiotensin-converting enzyme (ACE)] in a retrospective series of 144 RCCs, and the fluorimetric activity of these enzymes in prospectively collected serum of 128 RCC patients. The gene discussed is ACE; the disease is renal cell carcinoma.