Vicia graminea- and Vicia unijuga-binding glycoprotein (Vgu glycoprotein) has been reported as a malignant tumor-associated antigen, which is found in various kinds of malignant tumor-tissues and ascitic and cyst fluids of malignant tumor patients, but not found in 20 kinds of normal human tissues. The glycoprotein reacts with anti-N lectins of Vicia-graminea (VGA) and Vicia unijuga (VUA), but does not react with anti-blood group M and N sera. The existence of Vgu glycoprotein in human amniotic fluid is reported here. A perchloric acid-soluble glycoprotein fraction (PASF) was prepared from human amniotic fluid (AF-PASF). Sialoglycoprotein was then separated from AF-PASF by consecutive gel filtration on Sephacryl S-300, HPLC on Asahipak GS-710 and affinity chromatography in VUA-conjugated formyl-cellulofine columns. The sialoglycoprotein with 9.6% (w/w) carbohydrate content showed a molecular mass of 2940 kDa estimated by HPLC gel filtration. The sialoglycoprotein showed reactivity with VGA and VUA, but did not react with anti-M and -N sera. In addition, the sialoglycoprotein reacted with lectins of Ulex europeus, Arachis hypogaea, Maclura pomifera, Canavalia ensiformis, Ricinus communis, Phaseolus vulgaris, Sambucus nigra and Sophora japonica. These results show that Vgu glycoprotein exists in human amniotic fluid, and that Vgu glycoprotein obtained from human amniotic fluid has a similar serological property to Vgu glycoproteins found in malignant tumor-tissues, but its chemical property is significantly different from that of malignant-tumor associated Vgu glycoproteins.