Estrogenic pollutants have been the focus of numerous research undertakings in contemporary ecotoxicology. Exposure to these endocrine-disrupting compounds (EDCs) has caused reproductive impairment in vulnerable organisms. The presence of 17β-estradiol (E2), an estrogenic endocrine disruptor, has been confirmed in Laguna de Bay. Effects that corresponded to estrogen exposure in caged male fish were also observed (Paraso and Capitan, 2012). E2 is a pollutant of either human or animal origin that reaches the aquatic environment via untreated sewage effluent. The public health implications of EDC exposure have warranted the adoption of the “precautionary approach” for endocrine disruptors in advanced countries like US, Canada and Europe. In effect, relevant environmental policies and/or regulations have been implemented that would inhibit, if not, minimize the release of these compounds into the environment “in advance of scientific certainty to prevent harm to humans and the environment” (O'Riordan and Jordan, 1995). Most local freshwater systems serve as a sink to domestic, agricultural and industrial effluent. Coupled with the lack of sewage treatment plants in the country, contamination of bodies of water with estrogenic pollutants is highly probable but remains largely unstudied. However, in addition to screening surface waters for the presence of these compounds, assessing exposure impacts on the aquatic biota should also be endeavored. The use of biomarkers as tools for monitoring estrogenic contamination of aquatic ecosystems has gained popularity in recent years. Biomarkers are biochemical or cellular alterations that may be attributed to the occurrence and magnitude of toxicants; thus, may serve as early warning signals (van der Oost et al., 2003). Measurement and characterization of these biomarkers not only gauge overall fish health but also aid in the identification of pollution hotspots. There is currently a paucity of published data on the impact of estrogenic pollutants on aquatic organisms in the Philippines, particularly those measured by biomarkers. This research project was aimed at evaluating sensitive fish biomarkers that may be utilized as parameters to determine contamination of Laguna de Bay with environmental estrogens. Vitellogenin response, a biomarker of exposure to these compounds, were assessed in feral fish together with liver and gonad histopathology parameters, and gross indices such as the gonadosomatic index (GSI) and hepatopancreas-somatic index (HPSI). The information gained in this research is hoped to establish the applicability and sensitivity of biomarkers in measuring and assessing estrogenic contamination of local freshwater resources.