To the Editor.
—Recently, Nakai et al1 and Odagiri et al2 reported immunoreactive β-endorphin to be present not only in the hypothalamus and pituitary gland but also in the placenta.These results suggest that placental extracts (especially chorionic gonadotropin preparation) may contain immunoreactive β-endorphin as well. We tried to determine immunoreactive βendorphin content in a chorionic gonadotropin preparation (Pregnyl). The content of immunoreactive β-endorphin in the chorionic gonadotropin preparation was demonstrated as 266 pg/5,000 IU of chorionic gonadotropin per ampule. However, the dilution curve of the chorionic gonadotropin preparation didnot show a parallelism with the standard curve of β-endorphin. Odagiri et al2 also observed nonparallelism in the dilution curves of the placental extracts-1M acetic acid, glacial acetic acid, glacial acetic acid/acetone, and Payne's extraction procedures,3 although parallelism was found with water extract of placenta.The analgesic effect of the chorionic gonadotropin preparation was clearly observed in our patients