& b u l l e t ; ABSTRACTThe question is posed: why were two pesticides, Aldrin and Dieldrin, judged to be carcinogenic in the US but not in Britain when the same evidence was available to the public authorities in both countries? No single cause is identified; rather, a variety of mutually reinforcing factors account for the decisions by the two public authorities: the uncertainty of the scientific evidence; the application of different standards of carcinogenicity associated with different social and scientific commitments; the government agencies with primary responsibility for the decisions; the way in which pesticides are regulated; and several cultural and economic considerations. The case study illustrates the analytical inadequacy of the fact-value distinction, and the tendency of decision-makers to justify their decisions by recourse to science. It also supports the view that the traditional relationship between science and public policy is being redefined in complex, technical areas of decision-making like risk assessment.The nature and scale of the hazards associated with new technologies have required governments to make difficult decisions about the form of control they should exercise over new products and processes. Although governments have received advice from a large and growing body of scientists, this has not always simplified the decision-making process nor rendered it more rational and objective. In this paper, we try to explain why two governments reached contradictory conclusions to the same problem on the basis of the same scientific evidence. More specifically, we will try to explain why two chemical pesticides, Aldrin and Dieldrin