In Brief OBJECTIVE To compare hCG levels, obtained by biologic and immunologic means, in women with normal pregnancies and women with preeclampsia. METHODS Peripheral blood samples from women in the third trimester with preeclampsia (n = 30) or normal pregnancies (n = 30) were assayed for immunoactive and bioactive hCG (mouse Leydig cell testosterone production assay). RESULTS Serum bioactive hCG levels tended to be lower than normal, and immunoactive hCG levels tended to be higher in women with preeclampsia, but the differences were not statistically significant. However, the ratio of bioactive to immunoactive hCG was significantly lower than normal for preeclamptic women (0.71 ± 0.28 vs. 1.15 ± 0.35 for normotensive pregnant women [mean ± standard deviation], P < .001). CONCLUSION The ratio of bioactive to immunoreactive serum hCG is lower among preeclamptic than among normotensive pregnant women. The ratio of bioactive to immunoactive hCG in women with preeclampsia is lower than normal.