Recent reports provide evidence that cancer is frequently associated with malnutrition and infection. This is particularly evident when the gastrointestinal tract is involved. The purpose of this study is to investigate the difference between the nutritional status of patients with gastric cancer and with peptic ulcer, and to determine which of the nutritional indicators may be of value in identifying patients with high risk of postoperative infections. A complete nutritional assessment was performed at admission and the following parameters were determined: hemoglobin, total serum protein, albumin, ceruloplasmin, retinol binding protein, transferrin; Fe; urine creatinine, creatinine/height index, arm muscle circumference; ideal body weight, usual body weight, arm circumference, triceps skinfold; lymphocytes, white blood cells, C3c, skin tests to recall and primary antigens. In the cancer patient group, hemoglobin, total protein, albumin, Fe, percentage usual body weight, and delayed hypersensitivity response to skin antigens were significantly more impaired than in controls. Preoperative delayed hypersensitivity response was the only test in correlation with the tumor stage. It was also significantly different in the gastric cancer patients who developed postoperative infections.