This thesis examines the origins of estrogen related HEM as a science-policy concept that emerged during a period of socio-political ambiguity in the 199Os. The thesis tracks a complex pattern of reciprocal influence between science and policy (mainly European) in the regulation of synthetic chemicals, low dose exposure, and HEM - with reference to BPA. Specifically, the thesis demonstrates that precautionary appraisal procedures changed the involvement and weighting of basic science in decision-making processes. From this position it suggests that the precautionary principle (PP) made regulatory knowledge processes for chemicals more reflexive to experimental hypotheses relating human health to environmental estrogens. It is argued that by harnessing basic science in this way to address user-oriented issues, the PP evolved a highly reflexive science-policy model with analytic and deliberative procedures to drive, produce, distribute and evaluate scientific knowledge. However, the dynamics provoked by these procedures (arOlmd EM theory) caused the system to oscillate between different states of nomological possibility and epistemic risk which, for chemicals like BPA, broke down to perpetuate an indefinite cycle of research. It appears that this cycle becomes harder to break when technical and social uncertainties act together to motivate further research so that the system becomes almost selfregulating, building a 'body of knowledge' around a perceived problem (male reproductive disorders). In conclusion the thesis argues that the societal response to chemical concerns stimulated a different form of scientific and social scrutiny, reflexive to the motivations and perspectives of precautionary policy, scientific conjecture, and public perception. This changed the nature of technical evidence counting as policy relevant knowledge, which has made it difficult to bring closure to the hazard assessments associated with BP A, and indicates the potential for future difficulties in regulatory science.