To investigate the expression of ICAM 1 in peripheral blood lymphocyte in elderly patients suffering from lung cancer and the effect of chemotherapy on the expression of ICAM 1, peripheral blood ICAM 1 contents in 52 elderly patients with lung cancer were assayed with the method of immune flow cytometry before and after chemotherapy, and 32 normal elders and 35 patients with benign disease in lung served as controls. The results showed that the expression of ICAM 1 on lymphocyte in elders with lung cancer was significantly higher than that in patients with benign disease and normal controls. There was a significant difference between ICAM 1 expression in patients in stage Ⅲ, Ⅳ and that in patients in stage Ⅰ and Ⅱ. ICAM 1 in peripheral blood before chemotherapy was significantly higher than that after chemotherapy. It is suggested that the expression of ICAM 1 in peripheral blood lymphocyte might be useful to judge the efficacy of chemotherapy and evaluate prognosis in geriatric patients with lung cancer.