The mouse monoclonal antibody P4-5C produced by Akihiko Kimura et al. is proved to be useful for the identification of human saliva, irrespective of the ABO blood group and secretion status, in medico-legal examinations. The antigen for the P4-5C are considered to be on the core protein of blood group substances, mucin type glycoprotein, in saliva, but not clearly elucidated yet. The ABO-blood group active glycoprotein was isolated from ethanol precipitates of boiled human saliva (A,Se), which was subjected to neuraminidase digestion, reduction and carboxymethylation (BSRCM). The excluded fraction (T-1) of the TPCK-tryptic digest of BSRCM from Superose 6 chromatography was positive for P4-5C as well as anti A,but negative for CBB protein staining. Chemical deglycosylation by periodate oxidation followed by beta-elimination of T-1 (OxE) did not affect the antigen of T-1 for P4-5C.However, further deglycosylation with trifluoromethanesulfonic acid at 0ﾟC,for 4hrs (DG) turned the antigen for P4-5C out. Amino acid and hexosamine analyzes of T-1, OxE and DG1 were carried out. These results suggest that the carbohydrates remained in OxE keep specific cluster of carbohydrates as the antigen for P4-5C and P4-5C was most likely directed to a carbohydrate determinant other than protein core. Amino acid composition of DG was typical one for mucin protein backbones which contain a high content of Ser, Thr, Pro, Ala and Gly. The DG was fractionated by Superose 12 chromatography. N-terminal amino acid sequence analysis (1-14) of the main fraction (DG1) was tried. However, a definite N-terminal sequence was not obtained by this experiment.