It has been demonstrated that human chorionic gonadotropin (hCG) inhibits HIV production in vitro, suggesting that this soluble placental glycoprotein can control viral replication and spread in vivo, hCG - the major product of fetal trophoblasts - was tested on an in vitro model consisting of choriocarcinoma-derived ENAMI trophoblasts exposed to HIV-infected MOLT-4 lymphocytes. The results show a U-shaped antiviral dose- effect and suggest that hCG may contribute to protection against intrauterine transmission of HIV-1.