We investigated the presence of KITM541L in five males with chronic eosinophilic leukemia, not otherwise specified (CEL, NOS), all negative for Platelet-derived growth factor-alpha (PDGFR) or PDGFRbeta abnormalities, which responded to imatinib therapy. The gene discussed is PDGFRB; the disease is Chronic Eosinophilic Leukemia, Not Otherwise Specified.