In normal erythropoiesis, erythroid progenitors differentiate and proliferate in response to stimulation by erythropoietin (Epo). Epo binds to its receptor, EpoR, constitutively expressed at the surface of committed erythroid progenitors and induces homodimerization. This study is designed to evaluate the EpoR cDNA sequence and its level of expression in the clonal erythroid progenitors of MDS patients (in cells stratified for the same degree of erythroid maturation) to determine whether mutations in the EpoR may be responsible for an aberrant Epo signal transduction in MDS. As well as analyze intrinsic erythroid Epo expression to determine whether it differs between normal controls and patients with MDS and perform a microarray analysis of genes associated with Epo signal transduction to determine if MDS patients have abnormal expression of signal transduction proteins.