Two first cousins with thalassemia and with a paravertebral mass had had an indium 111 chloride bone marrow scan. Result of scan influenced therapy: medical treatment in one case where an extramedullary erythropoiesis was confirmed, surgical treatment in the other case. The use of dual-isotope SPECT (indium 111 chloride, HDP- 9 9 m Tc) constitutes a contribution to the establishment of diagnosis of extramedullary erythropoiesis, giving to bone marrow scintigraphy a merited importance, avoiding the biopsy.