The purification of prolactin is simplified by the strong binding of the hormone to pituitary tissue. An extreme alkaline or acidic pH is required to effectively extract prolactin and this provides a convenient way of removing a large number of serum and pituitary proteins by an initial extraction near neutrality. The first extraction can be made by homogenization of pituitary glands with O.9% saline (Lewis, Singh, and Seavey, 1971) which is effective for glands of both mammalian and non-mammalian species, or various acidic buffers can be used (Ellis, Grindeland, Nuenke, and Callahan, 1969; Hwang, Robertson, Guyda, and Friesen, 1973). After the initial extraction, prolactin is recovered by treating the tissue with an alkaline buffer (pH 10-11), either aqueous or ethanolic (Ellis et al., 1969; Lewis, Singh, and Seavey, 1972a; Hwang et al., 1973), since prolactin is soluble in this concentration of organic solvent so significant purification can be achieved in a single step. Prolactin can also be extracted from pituitary tissue at acidic conditions (pH 2-3) but this method has not been used frequently. The procedure of Lyons (1937) is the best example of this type of extraction.