Based on the previous data which indicated a preoperative decrease in cell-mediated immunity (CMI) is associated with the occurrence of infectious complications following surgery on patients with esophageal cancer, we examined possible factors contributing to a decrease in CMI levels. A multiple linear regression analysis was made on data from 76 patients with esophageal cancer and 53 with gastric cancer as the control. In patients with esophageal cancer, both protein-calorie malnutrition (PCM) and age factor contributed to a decrease in CMI, although the contribution of the latter was weak while the stage of the cancer and the grade of dysphagia showed no such contribution. The PCM and stage of the cancer were contributing factors in patients with gastric cancer. Thus, these results indicate that PCM and old age, and not the presence of malignant tumors, play a significant role in deficiency in CMI in patients with esophageal cancer.