A comparison has been made of three models which attempt to predict the dispersion of pollutants in situations with complex terrain. The three models are (1) a Gaussian calculation with terrain assumptions known as the NOAA model, (2) an EPA model, C4M3D also known as the 'valley' model, which substitutes different terrain assumptions in the Gaussian calculations, and (3) the INTERCOMP combined wind flow and plume dispersion model which uses a numerical calculational method. Predictions made by each of these models are compared to measurements of ambient concentration data taken in Huntington Canyon, Utah and at El Paso, Texas. The results indicate that the INTERCOMP model has a predictive accuracy for terrain situations comparable to that normally expected for Gaussian predictions in flat terrain, i.e. a factor of two to three. For stable atmospheres, however, the Gaussian predictions of the NOAA model averaged a factor of fifteen higher than the measured results.