Using an indirect immunofluorescent assay with mouse anti-human monoclonal antibodies of OKT_3, OKT_4, OKT_8, we investigated the sequential changes of peripheral blood T lymphocyte subsets in 30 patients with lung cancer or esophageal cancer, and 16 with non-cancerous thoracic disease before and after operation, and in 15 healthy persons as a control group. The data from the cancer patients showed that the number of OKT_4 cells was lower, whereas that of OKT_8 cells was much higher, and the OKT_4/OKT_8 rat...