A case of a normal pregnancy and delivery with extremely low placental lactogen hormone (hPL) values in maternal blood is presented. The low hPL-values were due to the fact that the placenta only produced about 1/25 of the normal estimated output, calculated on the basis of the hPL-concentration in the intervillous spaces. The concentrations of progesterone, the placenta-specific beta-glycoprotein (SP1) and total estriol in serum were normal, while prolactin and chorionic gonadotropin (hCG) were considerably elevated. Glucose levels were normal. At the ultrastructural level the actual placenta under study did not differ from a normal term placenta. In spite of the very low concentrations of hPL there was a good milk secretion, and the mother was still breast-feeding her baby 11 months after the delivery. Basal level of prolactin was at this time normal.