Thyroxine-binding globulin (TBG), thyroxine-binding prealbumin (TBPA), thy-roxine (T4), free T4, triiodothyronine (T3) and thyroid-stimulating hormone (TSH) were studied in 144 apparently healthy, euthyroid pregnant women displaying miscarriages. In an additional group of 18 aborting women a frozen blood sample drawn in early pregnancy was similarly analyzed for the thyroid components as well as for human chorionic gonadotropin (HCG). The values were compared to those of normal pregnancies (n = 228) at corresponding intervals. Significantly lower values of TBG were found in the spontaneously aborting women. Slightly lower values were found concerning T4 and T3 in the spontaneously aborting group. A significantly lower value of TBG was found to be more predictive concerning spontaneous abortion than that of HCG.