Efforts have been directed toward partial purification and identification of a reversible decapacitation factor from rabbit seminal plasma. Five fractions were consistently obtained following fractionation of rabbit seminal plasma on a Sephadex G-200 column. Only the first two fractions had decapacitation factor (DF) activity. On SDS polyacrylamide gel electrophoresis, several carbohydrate-and protein-containing components were found in each fraction from the Sephadex column. Further, DF activity could be obtained in the precipitate resulting from cetyl pyridinium chloride (CPC) treatment of the active fractions from the Sephadex G-200 column. In the comparison of the components observed with SDS gel electrophoresis throughout these fractionation procedures, the reversible decapacitation activity appeared to be associated with a component containing protein and carbohydrate. From these studies, then, reversible decapacitation activity of rabbit seminal plasma appears to be associated with a glycoprotein of an approximate molecular weight of 115,000.