Factor VIIIR:Ag and Factor VIII:C levels were found to be significantly increased during pregnancy, labor and puerperium, but not to the extent observed by European and American authors. The ratio Factor VIIIR:Ag/Factor VIII:C was elevated only between the third and sixth hour of labor with respect to early labor, and during parturition and early puerperium with respect to late labor. However, this ratio was in the same range as the normal non-pregnant controls, but in the cases of complicated pregnancy, the ratio reached values much higher than the normal. It was concluded that determination of the ratio appears to be of little value in normal cases but may be of use when there are obstetrical complications. Studies are being performed to try to explain the limited rise in Factor VIII:Ag and Factor VIII:C levels observed in our cases.