Our experience with 185 cases of T-cell dominated skin infiltrates demonstrates that the PCR-based method for detection of TCR gamma chain gene rearrangement in combination with temperature gradient electrophoresis can routinely be used for the demonstration of clonal T cells in formalin-fixed and paraffin-embedded biopsies of lesional skin. In contrast to Southern blot analysis, the amplification by PCR is nonradioactive, is not time consuming (approximately 3 days), can be performed using frozen or paraffin-embedded tissue, and allows additional molecular biologic analyses, such as sequencing. Furthermore, it offers the possibility to design patient-specific primers for monitoring of the disease activity. It also has to be concluded from our study that all available clinical, histologic, cytologic, immunophenotypical, and rearrangement studies have to be considered in order to establish the correct diagnosis.