To demonstrate the ability of Fusion FISH to detect fusion transcripts in Ewing's sarcomas, two differently colored probe sets were prepared, one set, labeled with Alexa Fluor 594, was specific for the 5′ region (exons 1 to 5) of EWSR1 mRNA, and the other set, labeled with TMR, was specific for the 3′ region (exon 9) of FLI1 mRNA. This evidence concerns the gene EWSR1 and Ewing sarcoma.