CAT and major depressive disorder: In the present study, we found the following: (1) SOD levels were lower in both trBD mania and trBD depression than in controls, while GSH-Px and MDA levels were higher in both trBD mania and trBD depression than in controls; (2) CAT levels were positively associated with HAMD-17 scores in patients with trBD depression; and (3) MDA levels in trBD decreased significantly after 6 weeks of ECT.