Although preeclampsia represents a major threat for many pregnant women, the pathogenesis of this complication is far from being clear. Recent studies suggest that preeclampsia is an autoimmune disorder. Auto-antibodies against angiotensin receptor might explain some of the pathologic findings associated with preeclampsia. However, the origin of the autoimmune reaction is unknown. Here we hypothesize that circulating fetal RNA in maternal plasma might transfect maternal cells. Expression of fetal specific sequences could lead to an immune reaction breaking the immune tolerance against some antigens. Male fetus bearing pregnancies could be at higher risk of preeclampsia due to expression of Y-specific transcripts. This hypothesis is testable by analyzing antibodies and T-lymphocytes of pregnant women with male and female fetuses.