In a prospective study of women in the first trimester who were at risk for recurrent abortion, data from 20 pregnancies with normal outcomes were contrasted with those of 9 pregnancies that aborted spontaneously between 7 and 12 weeks. In pregnancies in which an embryo was present before abortion, the mean concentrations of human chorionic gonadotropin beta-subunit (hCG-beta) were low with a steady decline in progesterone levels, whereas estradiol (E2) and prolactin concentrations approximated those in normal pregnancies. With growth disorganization, mean hCG-beta, E2, and progesterone levels were significantly lower than normal. In 87.5% of embryopathic pregnancies, conclusive evidence of this disorder was obtained with ultrasound monitoring. Subnormal levels of hCG-beta, E2, and progesterone were observed in 88.9, 100, and 57.1%, respectively. The karyotype was abnormal in 80% of embryopathic pregnancies successfully cultured. The normal production of E2 appeared dependent on the presence of the embryo in the first trimester of pregnancy. Endocrine failure of the trophoblast and/or the corpus luteum in embryopathic pregnancy is suggested by diminished hCG-beta and progesterone concentrations. Serial ultrasound scanning and hormone assay, particularly of hCG-beta and E2, may be useful in assessing pregnancy at risk for recurrent abortion. However, because subnormal hormone levels may occur relatively late in the clinical course of embryopathic gestation, ultrasound scanning may yield more useful results as compared with hormone assay. Further studies are required to define more clearly the mechanisms of endocrine failure in embryopathic pregnancy.