r-Glutamyltranspeptidase (r-GT) from a rat hepatoma induced by 3'-methyl-4-dimethylaminoazobenzene (3'-Me DAB) was purified 833 fold. The purified enzyme had a specific activity of 15.0 U/mg protein with an overall yield of 3.8%. The molecular weight of native r-GT was estimated as about 350,000 daltons, whichs a multicomplex of a single polypetide having a M W of 59,000. Anti r-GT rabbit antiserum cross-reacted with kidney r-GT as well as liver r-GT. Tryptic digestion of r-GT followed by separation with Con A sepharose column chromatography resulted in two major glycopeptides. A tumor associated antigen was prepared by the conjugation of a tryptic glycopeptide of r-GT to keyhole limpets hemocyanin and an antibody against this antigen cross-reacted preferentially with r-GT in rat hepatoma tissue.