A 39 year old patient diagnosed of severe aplastic anemia and treated with allogenic bone marrow transplantation and who presented chronic eosinophilic pneumonia eight months after the transplant is presented. The patient had no previous history of asthma or atopy. Conditioning was performed with cyclophosphamide and total body irradiation. Prophylaxis of the graft versus host disease was carried out with cyclosporin and short course of methotrexate. At day 30 mild graft versus host disease appeared which spontaneously resolved. A progressive increase in the number of eosinophils was observed from day +40 reaching 1.05 x 10(9)/l at day +180 coinciding with suspension of the cyclosporine. The patient remained asymptomatic with no evidence of chronic graft versus host disease. At 8 months following allogenic transplantation the patient developed three episodes of fever, cough, moderate dyspnea and pulmonary infiltrates. Respiratory tests showed a restrictive pattern. Bronchoalveolar lavage contained 20% of eosinophils. Upon lung biopsy alveolar infiltration by eosinophils, lymphocytes and mononuclear cells was observed. Diagnosis of chronic eosinophilic pneumonia was made with initiation of steroid treatment. A drastic response was observed. The patient remained asymptomatic without recurrence and without evidence of chronic graft versus host disease. This picture may have been caused by the donor eosinophils given that retrospective evaluation demonstrated a persistent moderate eosinophilia in the donor.