FasL molecule expressed on activated T cells induces apoptosis in Fas-expressing cells. It is possible that apoptosis induced by FasL is involved in the process of allograft destruction brought about by infiltrating T cells. The aim of our study was to evaluate expression of FasL gene in peripheral blood T cells of renal allograft recipients (RAR). We have studied 25 patients: 16 with uneventful stable course (RAR-S) and nine during biopsy proven chronic rejection (RAR-CH). The relative expression of FasL mRNA compared with that of beta-actin was established by semi-quantitative RT-PCR. We have found that FasL gene expression was significantly increased in T cells of RAR-CH compared to RAR-S (P<0.01). Our results suggest that T cell expression of FasL gene is increased during chronic rejection. Therefore, this phenomenon may pay a role in allograft injury associated with that process. Further studies are needed to unravel possible clinical consequences of observed differences in T cell expression of FasL.