A patient is presented with Whipple’s disease. Before treatment, Haemophilus influenzae type e, sensitive to tetracycline was cultured from multiple small intestinal biopsies. This isolated micro-organism was structurally similar to the one observed in the tissue. All further culture experiments during and after treatment proved negative except for one biopsy from which a tetracycline-resistant H. influenzae type-e mutant was isolated. The immunological disturbances, mainly characterized by cutaneous anergy, in absence of major humoral or in vitro lymphocytic impairment, regressed during treatment together with clinical remission of the disease. These findings are considered in favour of the secondary nature of the immunological abnormalitie