We investigated surface markers of lymphocytes infiltrating four different histological non-small cell lung cancer tissues obtained at surgery and the corresponding peripheral blood lymphocytes (PBL) of 40 clinical cases, who had undergone no prior anti-cancer treatment, by flowcytometry. In estimation of the mean proportion of each lymphocyte subset, a paired Wilcoxon test revealed that tumor-infiltrating lymphocytes (TIL) exhibited significantly higher values of CD3+ cells (P < 0.05), CD8+ cells (P < 0.05) and CD20+ cells (P < 0.01), and lower value of CD16+cells (P < 0.05), as compared with those in PBL. The Spearman test revealed that none of the values of surface markers in TIL statistically correlated with those in the corresponding PBL (r < 0.6, P > 0.05). Although there was no significant difference between the mean CD4/CD8 ratio of total TIL and that of PBL, TIL of 12 patients with squamous cell carcinoma almost always showed lower values of CD4/CD8 ratio than those in PBL (P < 0.05), while the CD4/CD8 ratio was similar between TIL and PBL in adenocarcinoma. These results suggest that TIL of lung cancers represent specific immunological responses, whose characteristic depend on the histological types of lung cancers.