It was believed for a long time that functional LH/hCG receptors were present only in gonads. Recent studies have demonstrated, however, that these receptors are also present in several nongonadal organs in the human body. Uterus is one of them. Besides two uterine layers, endothelial cells and smooth muscle of blood vessels in the uterus also contain these receptors. In vivo administration of hCG decreased vascular resistance in the human uterus and in vitro treatment increased vasodilatory and decreased vasoconstrictive eicosanoids in the vessels. These findings led us to investigate whether hCG administration to patients with signs of threatened abortion has any beneficial effect. Patients were treated with either magnesium or progesterone and/or hCG. The results showed that the frequency of patients reaching second trimester was higher when hCG was used, which was paralleled by a significant decrease in uterine vascular resistance. Patients who reached term after treatment had decreased incidence of preterm delivery and intrauterine growth retardation. In conclusion, we suggest that uterine vascular LH/hCG receptors play an important role in the peri-implantation period by increasing uterine blood flow through vasodilatation and also perhaps through angiogenesis and trophoblast invasion, resulting in therapeutic benefit.