The US Nuclear Regulatory Commission (US NRC) is interested in uncertainty aspects of all phases of probabilistic risk analysis for nuclear power plants, including uncertainty related to atmospheric transport and deposition of radionuclides resulting from an accidental release. The US NRC has made significant investments in developing probabilistic computer models of atmospheric transport and deposition. The MACCS2 code is the primary code used to estimate the off-site consequences and uncertainty from atmospheric transport and deposition of radionuclides, as well as several other factors of importance. The US NRC has also invested significantly in processes to estimate and bound uncertainties. The collaborative project between the US NRC and the Commission of European Communities (CEC) to provide expert elicitation of uncertainties in several aspects of consequence calculations was a major effort throughout the mid-1990s to better understand the uncertainty associated with parameters used in off-site consequence models. The US NRC has used uncertainty data generated by this expert elicitation process as input to the MACCS2 code to help understand the implications of the expert data on the resulting uncertainty of consequence calculations. This paper describes the analyses designed to incorporate the uncertainties estimated by the NRC/CEC experts and transformed for use in the MACCS2 code. Issues encountered and insights gained from this experience are presented and discussed.