Background: Human milk (HM) fortification has been recommended for the nutritional optimization of very low-birthweight infants. This study analyzed the bioactive components of HM and evaluated fortification choices that could accentuate or attenuate the concentration of such components, with special reference to human milk-derived fortifier (HMDF) offered to extremely premature infants as an exclusive human milk diet. Materials and Methods: An observational feasibility study analyzed the biochemical and immunochemical characteristics of mothers' own milk (MOM), both fresh and frozen, and pasteurized banked donor human milk (DHM), each supplemented with either HMDF or cow's milk-derived fortifier (CMDF). Gestation-specific specimens were analyzed for macronutrients, pH, total solids, antioxidant activity (AA), ¿-lactalbumin, lactoferrin, lysozyme, and ¿- and ß-caseins. Data were analyzed for variance applying general linear model and Tukey's test for pairwise comparison. Results: DHM exhibited significantly lower (p¿<¿0.05) lactoferrin and ¿-lactalbumin concentrations than fresh and frozen MOM. HMDF reinstated lactoferrin and ¿-lactalbumin and exhibited higher protein, fat, and total solids (p¿<¿0.05) in comparison to unfortified and CMDF-supplemented specimens. HMDF had the highest (p¿<¿0.05) AA, suggesting the potential capability of HMDF to enhance oxidative scavenging. Conclusion: DHM, compared with MOM, has reduced bioactive properties, and CMDF conferred the least additional bioactive components. Reinstatement and further enhancement of bioactivity, which has been attenuated through pasteurization of DHM, is demonstrated through HMDF supplementation. Freshly expressed MOM fortified with HMDF and given early, enterally, and exclusively (3E) appears an optimal nutritional choice for extremely premature infants.