Ewing's sarcoma is a poorly characterized malignant tumor with a relatively uniform histologic appearance, made up of densely packed small cells with round to oval nuclei, without distinct cell borders and without any structural differentiation. Often the diagnosis has to be made by exclusion. Recently, it has been made possible to identify characteristic chromosomal rearrangements associated with certain solid tumors. More than 85% of Ewing's sarcoma and peripheral neuroectodermal tumor present a specific t(11;22)(q24;q12) balanced translocation, resulting in the production of a novel chimerical EWS/FLI-1 message. Using oligonucleotide primers derived from EWS and FLI-1 complementary DNAs, we were able to use reverse transcription-polymerase chain reaction (RT-PCR) as a diagnostic tool. The described nested RT-PCR method as another supportive diagnostic method enables pathologists to differentiate small blue cell tumors not only to make correct diagnosis but also to investigate retrospective archival tumor samples, using formalin fixed paraffin embedded tissue as a source of RNA.