The project reports the identification in oral fluid samples of preterm newborns of AHSP (Alpha-hemoglobin Stabilizing Protein), an erythroid-specific protein forming stable complexes with free α-hemoglobin preventing its harmful aggregation and pro-oxidant activity during red blood cell development, following nanoHPLC-high resolution MS proteomic analysis in top-down approach and the determination of its primary structure. Full scan MS spectra deconvolution revealed a monoisotopic mass of the protein inconsistent with the previously reported sequence. The analysis of the MS fragmentation spectra of the protein multicharged ion at 980.29 m/z [M+12H]12+ evidenced a shift of the experimental b-ions which extended from the amino terminus, suggesting the presence of an N-terminal modification in the protein, i.e., the elimination of the iMet1 and the acetylation of the Nα-terminal Ala2, which was confirmed by comparison of the theoretical and experimental MS fragmentation pattern.