Prognostic assessment provides information on environmental behavior of chemicals when no direct information exists. The utility of this method of analysis depends on the way in which the prognostic modeling tools are used. When the environment and the properties of the chemical are both well known, specific results of a valid exposure analysis model can be accepted with reasonable confidence. Generally, however, adequate information is not available on the chemical properties. Thus, it is more reasonable to seek bounds on the expected behavior of the chemical based on uncertainties in these properties than to place credibility on any specific result. These kinds of results of prognostic assessment provide an efficient means to direct further efforts to obtain specific information of direct benefit for regulatory decisions. The utility of the prognostic assessment concept lies, therefore, in its use in a hierarchial evaluation scheme in which available information is used to move efficiently to subsequent tiers.