The role of the macromolecular constituents of human oviductal fluid (hOF) in reproductive physiology is poorly understood. Oviductal fluid contains proteins derived by transudation from serum and those synthesized and secreted by the tubal mucosa. In this communication, we describe purification of hOF-specific proteins. As a first step, serum proteins were removed with an immunoaffinity gel. Fractionation of the proteins unique to hOF was accomplished with DEAE-cellulose chromatography. One of these proteins was obtained in a highly purified state after gel filtration on G-75 Sephadex. This protein of 54 kDa molecular weight had a pI of 4.5 and contained carbohydrate. We propose that this hOF glycoprotein be designated "human oviductin I" (hOV I).