Abstract. To reveal the intracellular signal transduction molecules involved in granulosa cell apoptosis in porcine ovarian follicles, we cloned the porcine Fas-associated death domain (FADD), an adaptor protein for the cell death receptor, and procaspase-8, an initiator caspase. Porcine FADD (pFADD) was 636 bp (211 amino acids: aa) long and showed 74.0 and 65.4% homology with human and murine FADD, respectively. Porcine procaspase-8 (pprocaspase-8) was 1,431 bp (476 aa) long and 70.6 and 63.4% homologous with human and murine procaspase-8, respectively. To confirm the apoptosis-inducing abilities, we constructed pFADD and pprocaspase-8 cDNA expression vectors with enhanced green fluorescence protein (EGFP) and then transfected them into human uterine cervix tumor (HeLa-K), human granulosa cell-derived (KGN), murine granulosa-derived tumor (KK1), and porcine granulosa cell-derived (JC410) cells. When pFADD and pprocaspase-8 were overexpressed, cell death was induced in these transfected cells. However when caspase-inhibitor p35 was cotransfected, cell death was inhibited. The pFADD and pprocaspase-8 genes are well conserved, as are the physiological functions of their products. Key words: Apoptosis, Caspase-8, Fas-associated death domain (FADD), Granulosa cell, Porcine ovary (J. Reprod. Dev. 53: [427][428][429][430][431][432][433][434][435][436] 2007) poptosis is an important phenomenon involved i n c e l l s u r v i v a l a n d / o r d e a t h d u r i n g differentiation and development [1,2]. The death ligand and receptor systems are considered to be apoptosis-inducing factors [3][4][5][6][7]. Death receptors, which belong to the tumor necrosis factor (TNF) receptor family, are membrane-binding proteins with a death domain (DD) in their intracellular regions. An adaptor protein, such as Fasassociating death domain protein (FADD), which has a DD in the C-terminal region and a death effector domain (DED) in the N-terminal region, is recruited when each specific ligand binds to its r e c e p t o r [ 8 -1 0 ] . T h e n , F A D D b i n d s w i t h procaspase-8 (also called FLICE), which has two DEDs in the N-teminal region [11,12]. These molecules compose the death-inducing signaling complex (DISC). As a result of the proteolytic autoactivation of procaspase-8 [13], subunit protein 18 (p18) and 11 (p11) are released into the cytoplasm and reform a proteolytic component that c l e a v e s m a n y s u b s t r a t e p r o t e i n s , s u c h a s