We screened seven Tunisian patients fulfilling the WHO criteria of HES for the presence of the FIP1L1-PDGFRA fusion gene using nested reverse transcription polymerase chain reaction on peripheral blood samples.     ///    Detection of the FIP1L1-PDGFRA fusion gene or the corresponding cryptic 4q12 deletion in HES supports the diagnosis of chronic eosinophilic leukemia (CEL) and provides a molecular explanation for the pathogenesis of this disorder.     ///    FIP1L1-PDGFRA positive chronic eosinophilic leukemia in Tunisian patients..     ///    Splenomegaly was constant in FIP1L1-PDGFRA positive CEL but not in the other HES patients (only 1/3).. 