By using a method of electrophoresis separation, the authors determined the relative values of each one of the lactic dehydrogenase (LDH) isoenzymes in the normal colonic mucosa. In adenocarcinomas, there is a significant rise in the percent of LDH-5. A similar disturbance has been demonstrated in 14 polyps, which confirms the known precancerous condition of these lesions. In the uninvolved mucosa surrounding neoplasm, the authors found that the increase in the relative proportion of "type M" isoenzymes, starting at 2 cm from the edge of the tumor, progressively disappears as the sample are taken farther away from the neoplasm. The authors conclude that these LDH isoenzyme pattern shifts in a normal mucosa could be an early sign of malignancy before the morphologic changes and could also be of great interest in the prediction of cancer relapse in the suture line after surgery.