In this study, total cytoplasmic (Cu,Zn-SOD) and mitochondrial (Mn-SOD) superoxide dismutase activities were measured in sera and pleural fluids from patients with squamous cell carcinoma of the lung. The results were compared with those of control subjects and those of patients with tuberculosis and chronic heart failure. Serum activities were found higher in all patient groups compared to control group. Highest values were however in tuberculosis group. In the correlation analysis, meaningful intra- and inter-correlations were established between enzyme activities in the samples. Results suggest that high serum and pleural fluid SOD activities are not specific biochemical parameters for carcinogenesis and, activities may also increase in some other degenerative diseases such as tuberculosis, chronic heart failure, etc. Therefore, we believe that it is not useful to use serum and pleural fluid SOD activities for diagnostic purposes in cancer. However, the activities of these enzymes in the biological samples might be used as nonspecific prognostic markers in assessing cellular and mitochondrial tissue destruction.