The concentration of alpha 2HS-glycoprotein (alpha 2HS), a human homologue of the fetal protein fetuin, has been measured in plasma and cerebrospinal fluid (CSF) of fetuses from 14 to 37 weeks of gestation and in cord blood from newborn babies. The levels were highest in both plasma and CSF in the younger fetuses, but even in the newborn the concentration of alpha 2HS in plasma was nearly twice the adult level. Two of six fetuses in the 14- to 19-week group had levels of alpha 2HS over 200 mg/100 ml, which is similar to the levels of fetuin in some fetal animals.