[en] In this study, we report a clinical application of a rapid flow-cytometric immunofluorescence method for studying OKT11⁺-lymphocytes in whole blood by using monoclonal antibody OKT11. Changes in the relative percentages and absolute counts of OKT11⁺-lymphocytes during radiotherapy of cancer patients were evaluated by this method. In a study of 151 samples from 58 cases, the elevation of OKT11⁺-lymphocyte level (>=90%) was observed in 38 samples from 21 patients. Many cases of these responded well to radiotherapy. In contrast, the depression of OKT11⁺-lymphocyte level (<=70%) was observed in patients with poor response. The relative percentages of OKT11⁺-lymphocytes were consistent during radiotherapy, but absolute counts of OKT11⁺-lymphocytes were remarkably decreased during radiotherapy. In a study of 40 samples, the correlation coefficient between the manual E-rosette count and the flow immunofluorescence measurement was 0.8914. In a study of 132 samples, that between the absolute lymphocyte count and the OKT11⁺-lymphocyte count was 0.9673. (author)