The interplay between chemical risk assessment and scientific research is discussed in the context of recent attempts to improve the scientific basis for estimates of the human carcinogenic risk from methylene chloride. A combination of basic biochemical research and risk assessment oriented research, both mechanistic and pharmacokinetic, provided the initial impetus for re-evaluating the use of the default risk estimation approach. Resulting efforts to incorporate the new scientific information into the risk assessment process in turn identified specific additional research needed to reduce uncertainty in the estimated risk. This healthy interchange between the two disciplines has served both to refine the human risk estimates for methylene chloride and to more clearly identify key scientific issues for chemical risk assessment in general.