This study was to investigate the cytotoxic effects on pituitary adenoma cell lines GH3/MMQ/AtT20 induced by RGD-FasL and the underlying mechanism.Fas/DcR3 mRNAs were detected by RT-PCR and their surface expressions were measured by flow cytometry.Cytotoxicity exerted by RGD-FasL on tumor cells was measured with MTT assay and the induced apoptosis was determined by agarose gel electrophoresis. The celI cycle and apoptosis was assessed by flow cytometry with PI staining.The expressions of caspase8/9/3, Bcl-2, RANKL and JNK2 were detected by Western blotting.Approximately 13.7% of GH3 cells, 25.5% of MMQ cells, 22.2% of AtT20 cells express Fas. while 23.9% of GH3 cells, 24.1% of MMQ cells, 4.6% of AtT20 cells express DcR3.The cytotoxic effects of FasL, RGD-FasL on tumor cells were all taken in a dose-dependent manne. Cell lines MMQ/AtT20 showed the same sensitivity to RGD-FasL as to FasL, while celIIine GH3 was less sensitive to RGD. FasL. The cell cycle analysis indicated that RGD-FasL could inhibit cells in G0/G1 phase an d G2/M phase. In MMO and ART20 cells treated with RGD. FasL, the A1 was not significantly difierent from that treated with FasL, while in GH3 cells treated with RGD. FasL, the AI Was lower than that treated with FasL. The expressions of caspase. 8/9/3.RANKL and JNK2 were increased while that of Bcl-2 Was decreased after treatment with RGD-FasL, suggesting that RGD. FasL induces apoptosis through caspase activation. We concluded that RGD?FasL could possibly be considered as a novel therapeutical candidate for the treatment of pituitary adenomas. Cellular & Molecular Immunology.2008;5(1):61-68.