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Previously, we reported that we succeeded in isolating from human placenta a substance comparable to human renal nephritogenic glycoprotein prepared from glomerular basement membrane (GBM). This time we purified a sample isolated from human placental trophoblast basement membrane (TrBM) with the methods for purifying renal nephritogenic glycoprotein and clarified its chemical composition. To purify the sample prepared from human placental TrBM, we fractionated the sample by Zone Electrophoresis, Concanavalin A(Con A) affinity column chromatography and Bio Gel P200 column chromatography. As the active fraction of the sample purified from human placental TrBM bound specifically with Con A, it proved to be a glycoprotein. The monosaccharide composition of this glycoprotein was rich in glucose (glucose, galactose and mannose were in the ratio of 1.00:0.30:0.33) and the amino acid composition of this glycoprotein contained no collagenous components. Ouchterlony gel diffusion demonstrated the existence of a common precipitin line between antiserum to human renal nephritogenic glycoprotein prepared from GBM and human renal nephritogenic glycoprotein prepared from GBM, purified human placental glycoprotein, the sample prepared from human placental TrBM by sonication and nephritogenic glycoprotein prepared from urine of S.L.E. patient.