A 25-year-old patient presented with hypogammaglobulinemia diagnosed at the age of 7, causing recurrent infections of the gastrointestinal and bronchial tracts. He was treated with gammaglobulins and infusions of fresh human plasma. At admission he had an exacerbation of his chronic enteric symptoms. X-ray investigation and coloscopy showed mucosal changes as in enteritis regionalis . A biopsy of rectal mucosa showed accumulations of amyloid. Routine examination of humoral and cellular immune parameters revealed a pattern characteristic for common variable immunodeficiencies. Analysis of T-cell subsets with monoclonal antibodies of the OKT series showed unusually high relative numbers of OKT8+ cells (suppressor-T-lymphocytes) and a comparatively low number of OKT4+ cells (helper-T-lymphocytes). Suppressor-T-cells exert inhibitory effects on B-lymphocyte function (i.e. antibody production). The numerical excess of T-lymphocytes with suppressive properties could be a pathogenetically important factor with immunotherapeutic implications in a number of non-classifiable immunodeficiency syndromes.