Levels of activated factor XII (FXIIa) and VII (FVIIa) were determined in 100 women with uneventful pregnancies. Samples were divided into five study intervals: three during pregnancy, one at delivery and one 3 d postpartum. The median (range) for FXIIa levels were 3.4 ng/ml (1.2-9.1) from 11 to 20 weeks, 4.6 ng/ml (1.4-15.2) from 21 to 30 weeks, 5.4 ng/ml (1.9-14.3) from 31st week to delivery, 5.2 (1.3-11.4) at delivery and 4.3 (1.8-8.5) ng/ml in the postpartum sample. For FVIIa the median and range levels for the five periods were 4.9 (1.7-77.3), 7.2 (2.5-80.4), 11.1 (2.9-90.6), 12.0 (3.1-64.1) and 8.2 (4.0-23.5) ng/ml. Although the increase of FVIIa was higher than that of FXIIa during pregnancy, the overall changes of FXIIa and FVIIa were highly correlated (P<0.0001). At each time period the changes of FVIIa correlated with FVII:C which was not the case with FVII:Ag. These data indicate that during pregnancy both the contact phase and extrinsic pathway are activated.