To clarify the difference between gene expression signature of Epstein-Barr virus (EBV)-positive gammadelta T-cell lymphoproliferative disorders (LPD) and those in normal gammadelta T-cells, we set out to determine gene expression profiling using three gammadelta T-cell lines derived from patients with EBV-positive gammadelta T-cell LPD. Gene expression profiling using an Affymetrix Genechip revealed a unique gene expression pattern of NK cell receptors in gammadelta T-LPD cell lines. Genes encoding killer cell lectin-like receptors (KLR), such as KLRG1 and KLRB1 (CD161), were generally low in gammadelta T-LPD cell lines, while killer cell immunoglobulin-like receptors varied among cell lines. In addition, expression of CD161 surface antigen was found to be remarkably decreased in gammadelta T-LPD cell lines by flow cytometric analysis. We conclude that gammadelta T-cell expansion in EBV-positive gammadelta T-LPD is in part due to inappropriate expression of the NK cell receptors which related to impaired function cytotoxic T cells.