Abstract
A precipitating monospecific rabbit antiserum was produced by immunization with purified “pregnancy zone” protein. By means of double diffusion in agar gel 27 out of 30 pregnant women at term and 23 out of 30 women treated with oral contraceptives were found to have the “pregnancy zone” protein in their serum. The “pregnancy zone” protein was not detectable in 30 sera from non-pregnant women, 30 cord sera and 30 samples of amniotic fluid. A comparison between the electrophoretic and immunodiffusion methods for the detection of the “pregnancy zone” protein showed that the immunodiffusion method was about twice as sensitive as the electrophoretic method.