We report measurements of the concentration of NADH from malignant and non-malignant sites of tissues resected from patients suffering from cancer of the breast or oral cavity. The concentration of NADH was found to be significantly higher in malignant breast-tissue sites as compared with normal breast tissue, whereas the opposite result was obtained with malignant and normal tissues from the oral cavity. These results confirm the inferences made previously, from spectroscopic studies, and are consistent with other biochemical measurements reported in breast and oral cavity tissues.