Oxidant-antioxidant balance is known to regulate growth factors and invasion of tumor cells. Manganese superoxide dismutase (MnSOD), copper zinc SOD (CuZnSOD), and extracellular SOD (ECSOD), the first-line antioxidant defenses, were studied in lung carcinomas by immunohistochemical analysis (n = 139, 56, and 37, respectively) and in 8 lung tumor specimens by Western blot analysis and SOD activity measurement. Altogether, 49% of squamous cell carcinomas and 43% of the adenocarcinomas were positive for MnSOD by immunohistochemical analysis; corresponding values for CuZnSOD were 79% and 93%, respectively. MnSOD and CuZnSOD by Western blot analysis were 27% and 22% higher, and CuZnSOD activity was 93% higher (P = .06) in carcinomas than in nonmalignant lung tissue samples. ECSOD, a mainly extracellular enzyme, showed weak positivity only in 4 of 37 carcinomas, and by Western blot analysis showed 70% lower immunoreactivity (P