An emerging trend in risk assessment is to be more explicit about uncertainties, both during the analytical procedures and in communicating results. In February 1992, then-Deputy EPA Administrator Henry Habicht set out Agency goals in a memorandum stating that the Agency will present information on the range of exposures... and on the use of multiple risk descriptors and calls on analyses to be clearly delineating uncertainties and assumptions along with the impacts of these factors... on the overall assessment. These are restatements of existing principles, but the Agency is called upon to better bring them to fruition in its day-to-day practice. This would seem to require two areas of development: restructuring of institutional attitudes toward uncertainty and the development and acquisition of appropriate technical capabilities. Risk managers must value being presented with an array of information. They will still need to make specific regulatory 'calls', however. The challenge will be to establish agreed upon and legally supportable ways to make such determinations in the face of explicitly characterized uncertainties. EPA also faces the technical challenges of mounting the necessary efforts.