OBJECTIVE: To evaluate the association of antinuclear antibodies (ANA) with outcome of in vitrofertilization-embryo transfer (IVF-ET) as well as the effect of, short-term immunosuppression with prednisolone on implantation plantation, clinical pregnancy and live birth rates following IVF-ET. STUDY DESIGN: The study group consisted of 120 women, 22-42 years old, in whom IVF-ET was performed and whose ANA could be measured. Prednisolone (15-60 mg/d for 5 days) was administered starting 1 day after oocyte retrieval to some women with or without ANA, without randomization. The 223 IVF-ET cycles were divided into prednisolone-nontreated ANA-negative cycles, prednisolone-treated ANA-negative cycles, preduisolone-nontreated ANA-positive cycles and prednisolone-treated ANA-positive cycles. Retrospective analysis of rates of implantation, clinical pregnancy, and live birth were evaluated in the four groups. RESULTS: Overall, ANA positivity was noted in 20.0% of subjects, (24/120) and 25.1% of cycles (56/223). Implantation and clinical pregnancy rates in the prednisolohe-nontreated ANA-positive group were 0% (0/41 transplanted embryos) and 0% (0/15 cycles), significantly, lower than in the other groups. The live birth rate in Implantation, live birth rates low when this group was significantly lower than in-the prednisolone-non treated ANA.-negative group and non-significantly tended to be lower than in the other 2 groups. CONCLUSION: Implantation, clinical pregnancy and live birth rates following IVF-ET were. low when ANA was detected. Implantation and clinical pregnancy rates were improved significantly by prednisolone, but the live birth rate was not.