A 55-year-old male with a history of recurrent bacterial and viral infection was found to have hypogammaglobulinaemia in association with a benign thymoma. The patient lacked eosinophils and was deficient in basophils in both the peripheral blood and bone marrow. The absence of eosinophils in a skin challenge known to recruit these cells, and below normal total peripheral blood leucocyte histamine content further suggests a deficiency of eosinophils and basophils respectively. Abnormal suppressor T cell function was documented both phenotypically, using OKT monoclonal antisera, and functionally in pokeweed mitogen stimulated cultures. This patient is the first reported with a deficiency of both eosinophils and basophils occurring in the presence of hypogammaglobulinaemia and thymoma; these abnormalities may be related to the abnormal suppressor T cell function that is present.