Cytokines seem to play a critical role in the pathogenesis of unexplained recurrent pregnancy loss (RPL). Th1 cytokines have been shown to exert deleterious effects on pregnancy, inhibiting foetal growth and development. On the other hand, Th2 cytokines have been associated with successful pregnancy. The purpose of this study was to evaluate cytokine production in women with RPL. The studied group comprised 29 women with RPL, with at least three consecutive spontaneous abortions. The control group included 27 women with a history of successful pregnancies and no miscarriage. We determined IL-6 and TNF-alpha production in peripheral blood cultured with LPS, as well as IFN-gamma and TGF-beta induced by PHA stimulation. Cytokines were measured by enzyme-linked immunoabsorbant assay (ELISA) using commercial kits (RD, Amersham-Pharmacia). Mann-Whitney test was applied to compare differences between groups. The level of significance was defined at P < 0.05. We observed significantly higher levels of IFN-gamma (355.8 pg/ml versus 98.0 pg/ml; P = 0.01) and a trend toward increased TNF-alpha production (2410.2 pg/ml versus1980.2 pg/ml; P = 0.07) in RPL women as compared to controls. In relation to IL-6 and TGF-beta, no significant difference was detected between RPL and control groups. In agreement with experimental observations, our data support the hypothesis of Th1 cytokine involvement in the pathogenesis of RPL.