Products of tryptic hydrolysis of the maleic anhydride modified fragment Th3 from limited thermolytic hydrolysis of the G-factor have been studied. Some short peptides which result from the trypsin action on the native G-factor molecule and belong to the fragment T4 obtained on limited trypsinolysis of the G-factor have been separated and their structure has been studied. As a result amino acid sequence has been determined by tryptic peptides containing 322 amino acid residues of the fragment T4 which makes up about 94% of its polypeptide chain.