The usefulness of lymphocyte subset change as an indicator for predicting survival time and the effectiveness of combined treatment with an immunopotentiator, lentinan, and carboplatin (CBDCA) were investigated. Of 13 patients with advanced unresectable cancer entered in this study, 9 were administered 2 mg/body lentinan and 450 mg/m2 CBDCA, and 4 were administered a single modality of CBDCA. The mean survival time of all 13 cases was 9.89 months. Lymphocyte subsets of CD11(-)CD8(+), CD11(+)CD8(+), CD57(-)CD16(+) and CD57(+)CD16(+,-) were measured by two-color flow cytometry. In five cases surviving longer than 9.89 months, CD11(-)CD8(+)/CD11(+)CD8(+) on post-treatment showed an increase two-fold higher than on pre-treatment, but in all cases surviving less than 9.89 months the rate on post-treatment did not increase two fold higher than on pre-treatment. The mean (1.78) of (post-treatment/pre-treatment) ratios of CD57(-)CD16(+)/CD57(+) in long survival cases was significantly higher (p < 0.01) than that (0.46) in short survival cases. Moreover, the mean of (post-treatment/pre-treatment) ratios of CD11(-)CD8(+)/CD11(+)CD8(+) and CD57(-) CD16(+)/CD57(+) showed a good correlation with survival time. These results indicate that changes of lymphocyte subsets of killer T cell/suppressor T cell and natural killer cell on posttreatment compared to pre-treatment are clinically useful indicators for predicting and monitoring the effectiveness of combined treatment with lentinan and CBDCA.