Human placental lactogen (hPL), which was formerly referred to as ‘human chorionic somatomammotropin’, is a protein weighing 22 kD that shares some similarities with growth hormone. hPL can be identified in the maternal blood starting from the fifth week of pregnancy and plays a role in ensuring nutrient delivery to the developing fetus. The presence of anti-hPL reactions is observed in the syncytiotrophoblastic cells of the placenta and in choriocarcinoma.