Objective  To study effects of allogeneic blood transfusion on T-lymphocyte subset counts in gastric carcinoma patients. Methods  Thirty patients undergoing resection for gastric carcinoma,were randomly divided into three groups with 10 case each. Group A patients received no blood,Group B patients were transfused with leukodepleted blood and Group C patients were allocated to receiving allogeneic whole blood during perioperative period. Blood samples were taken before operation,on 2nd-,5th- and 10th day after operation. T-lymphocyte subsets were estimated by flow cytometry. Results  The T-lymphocyte subset counts was lower in gastric carcinoma patients than in normal controls(P<0.05). The CD3+ and CD4+ counts and CD4+/CD8+ ratio decreased after operation, but returned to the baseline levels on the 10th postoperative day. The CD3+ and CD4+ counts and CD4+/CD8+ ratio decreased significantly after operation in group B and group C, but not returned to preoperative level on the 10th postoperative day(P<0.05). As compared with that in group A, the CD3+ and CD4+ counts and CD4+/CD8+ ratio decreased markedly in group C than in group B (P<0.05). Conclusion  Perioperative blood transfusion contributes to the immunosuppression, which is more serious after whole blood transfusion than leukodepleted blood transfusion.  In perioperative period component blood transfusion is superior to whole blood transfusion. The decrease of the CD3+ and CD4+ counts and CD4+/CD8+ ratio may be one of the causes of immunosuppression in patients exposed to allogeneic blood transfusion.