Clinical staging and immune reactivity were correlated in 39 patients who underwent gastrectomy for primary gastric cancer. Cellular immunity was depressed as the stage of cancer advanced, whereas humoral immunity was unaffected. Gastrectomy for advanced cancer in stage 3 and 4 suppressed cellular immunity. The cellular and humoral immune systems in relation to total parenteral nutrition (TPN) versus non-TPN were evaluated in 57 patients who underwent gastrectomy for stage 3 and 4 advanced cancer. Cell-mediated immunocompetence was restored in all 29 patients who received postoperative TPN, while serum immunoglobulins were unaffected by TPN. Improvement of impaired cell-mediated immunity was also obtained in patients treated with a TPN-5-FU combination as an adjunct to surgery. Treatment with TPN during 5-FU administration restored immunocompetence, increased tolerance for 5-FU and gave a satisfactory 3-year survival rate. There were significant differences in the 3-year survival rates of patients who underwent non-curative gastrectomy (54 per cent for TPN-5-FU v. 0 per cent for non-TPN-5-FU; P less than 0.05). It is concluded that TPN during chemotherapy as an adjunct to surgery leads to diminished morbidity, and possibly to prolonged survival time, in patients undergoing gastrectomy for gastric cancer. A possible mechanism responsible for the gratifying results of TPN treatment may be the increased tolerance for 5-FU resulting from improved nutrition and increased cell-mediated immunity.