This study investigated the surface expression of the CD154 antigen (CD40L) on peripheral blood CD4+ T lymphocytes and the sera concentrations of soluble CD40L antigens (sCD40L) in non-pregnant women, normal pregnant women, and patients with pre-eclampsia. Twenty-five patients with pre-eclampsia, 18 healthy pregnant women, and 10 healthy non-pregnant women were included in the study. The expression of the CD154 antigen on CD4+ T lymphocytes was determined using flow cytometry. The serum concentration of sCD40L was measured using an ELISA. Statistical analysis was performed using the Mann-Whitney U and ANOVA tests. The expression of the CD154 antigen on CD4+ T lymphocytes and the serum concentration of soluble CD40L were significantly higher in pre-eclampsia than in normal pregnant women. In normal pregnancy the expression of the CD154 antigen on CD4+ T lymphocytes and the concentration of sCD40L were significantly lower than in non-pregnant women. We conclude that during normal pregnancy the levels of these inflammatory mediators are lower than in non-pregnant women. In pre-eclampsia the levels are higher than those in normal pregnancy, but stable compared with the non-pregnant state. These results suggest that in pre-eclampsia, there are disturbances in the mechanisms responsible for the decrease in innate immunity which occurs in normal pregnancy.