The fragile-X syndrome is a mental disorder caused by the absence of FMRP (the Fragile-X Mental Retardation Protein). While FMRP is found to be associated with the ribosomal components, its precise translational function remains to be defined. Here we report that FMRP is not found with the abundant free polysomes of the reticulocyte lysate, but rather with a heavy ribonucleoprotein complex sedimenting over 400S. This unusual distribution of FMRP at an advanced stage of mammalian erythropoiesis may unveil the discrete role of FMRP in translation.