A Japanese adult lacking the expression of HLA-A, HLA-B, and HLA-C antigens on the lymphocyte (the "bare lymphocyte syndrome") had recurrent sinopulmonary infections and diffusely progressive bronchiectasis. Class I antigen and beta 2-microglobulin on the lymphocytes of the patient, his siblings, his father, and healthy subjects were assayed by using monoclonal antibodies against these surface markers. Class I antigen and beta 2-microglobulin were not found on the lymphocytes of the patient and the Daudi cells. In addition, lymphocytes of his siblings showed low fluorescence intensity. The HLA molecule on the lymphocyte plays an important role at the stage of recognition of immunogenic antigens. These results might suggest a correlation between sinobronchiectasis and the deficiency of HLA molecules, and the importance of the HLA system in the immune defense mechanism.