Acid extract of human placental tissue contain, by both radioimmunoassay and radioreceptor assay, beta-endrophin-like material. Half of this material will not go through a 5000-dalton filter and on Sephadex G-200 has a molecular size between 25,00 and 50,000 daltons. Of the material going through a 5000-dalton ultrafilter, 80 percent is excluded on Sephadex G-25 and held back, very slightly, on Bio-Rad P6, indicating a molecular size of approximately 4500 to 4800 daltons. Thus, placenta appears to have macromolecular precursors from which a beta-endorphin-like material is released, with a size approximately 12 amino acids longer than half of the pituitary hormone.