Tumor necrosis factor-α (TNFα) has been shown to be a potent stimulator of prostaglandin (PG) F_2α synthesis in bovine endometrial stromal cells. The aims of the present study were to determine the effect of interferon-τ (IFNτ) on TNFα-stimulated PGF_2α synthesis and the intracellular mechanisms of TNFα and IFNτ action in the stromal cells. When cultured bovine stromal cells were exposed to TNFα (0.006–0.6 nM) for 24 h, the production of PGF_2α and cyclooxygenase (COX)-2 gene expression were stimulated by TNFα (0.06–0.6 nM, P < 0.05). Moreover, a specific COX-2 inhibitor (NS-398; 5 nM) blocked the stimulatory effect of TNFα on PGF_2α production (P < 0.05). Although IFNτ (0.03–30 ng/ml) did not stimulate basal PGF_2α production in the stromal cells, it suppressed TNFα action in PGF_2α production dose dependently (P < 0.05). Moreover, the stimulatory effect of TNFα (0.6 nM) on COX-2 gene expression was completely blocked by IFNτ (30 ng/ml; P < 0.05), although the gene expression of COX-2 was not influenced by IFNτ. The overall results indicate that the stimulatory effect of TNFα on PGF_2α production is mediated by the up-regulation of COX-2 gene expression and suggest that one of the mechanisms of the inhibitory effect of IFNτ on luteolysis is the inhibition of TNFα action in PGF_2α production in the stromal cells by the down-regulation of COX-2 gene expression stimulated by TNFα.