It is customary to portray risk regulation as a fixed regime of responsibility and rationality, predicated on the separation of risk assessment and risk management - a rule that took progressively took form in the 1980s in regulatory agencies such as the US EPA. Looking beneath the seemingly standard surface of designs for risk decision-making however, major inflexions may be detected in the way values are defined, uncertainty conceptualized, and responsibilities ascribed to scientists, officials or representatives of the public for addressing them. From this perspective, the risk-analytic approaches of the 1970s have little to do with the deliberative designs that emerged later in the 1990s. The shifts reflect the influence of successive risk public controversies, of the networks of experts that responded to these controversies, and their institutional inscription. Changes after or around Asilomar in ways of regulating risks, reflect the fact that Asilomar was but one site in the open institutional configurations in which risks were being regulated, and designs for science-policy regularly reinvented.