GPx activity has been studied in serum or plasma, erythrocytes, and neutrophils; total SOD, Cu,Zn-SOD and/or Mn-SOD levels or activities in serum or plasma, cerebrospinal fluid, erythrocytes, neutrophils, platelets, and lymphocytes; and catalase activity in erythrocytes from PD patients. Here, CAT is linked to Parkinson disease.