Depressed pregnancy-associated plasma protein A (PAPP-A) concentrations have been found in patients with threatened abortion, often weeks before spontaneous abortion while the fetus was still alive. In order to extend these findings we have developed a highly sensitive PAPP-A radio-immunoassay and have established a reference range in early pregnancy for PAPP-A between week 7 and week 20 of pregnancy, based on blood samples from 240 pregnant women. The gestational age was determined by ultrasound. PAPP-A was measured in 128 women admitted to hospital because of vaginal bleeding in the 7th to 20th gestational week. The viability of the fetus was confirmed by ultrasonography. The serum values of PAPP-A were significantly lower (p = 0.002) in the group of women with vaginal bleeding than in the group of normally pregnant women. However, with regard to abortion later on, the predictive value of an abnormal blood test on admission was only 18.7%. Serial determinations showed increased PAPP-A values corresponding to the centile expected in the 12 women who aborted, as well as in the 116 women who gave birth. Consequently, the test is of no clinical value in the assessment of the prognosis in patients with symptoms of threatened abortion.