A female patient with therapy-related acute non-lymphoblastic leukaemia occurring after intensive combined modality treatment for IIIB Hodgkin's disease was transplanted from her HLA-identical brother. No attempt was made to induce a remission and the transplant was performed with standard chemoradiotherapeutic conditioning. Three years after the transplant the patient is alive in complete remission with a 46,XY karyotype. The donor has a mild, heterozygous beta-thalassaemia ('thalassaemia minima'). The recipient has much more pronounced thalassaemic features, similar to so-called thalassaemia intermedia, with peripheral blood smears indistinguishable from thalassaemia major. The erythrocytic alterations are undoubtedly due to the splenectomy which was performed during a staging procedure, but the marked difference between donor and recipient haemoglobin values cannot be attributed solely to the asplenic state.