The analysis of the configuration of the immunoglobulin (Ig) and T-cell receptor (TCR) gene regions has been of great relevance in defining conclusively the nature of several lymphoproliferative disorders in man. Furthermore, this technological tool has also helped to dissect between a monoclonal and polyclonal pattern of proliferation. The major results obtained, the potential use of molecular studies for the detection of minimal residual disease and the relevance of these techniques in the understanding of the processes of leukemogenesis and lymphomagenesis are discussed.