“…The most likely explanation is that, despite fetal death, progesterone binding globulin (PBG) is still present in maternal plasma and thereby protects progesterone from degradation. These results contradict the supposition that a viable conceptus should be the stimu¬ lus for production of PBG (Illingworth et al, 1970;Milgrom et al, 1973;Heap & Illingworth, 1974;Evans et al, 1982), and determinations of plasma progesterone concentrations in the guinea-pig are clearly unreliable indicators of fetal viability. The present results provide no support for the hypothesis that an enzyme-induced decrease in plasma progesterone concentrations is the main cause of the fetal death observed in PCB-treated guinea-pigs.…”