The mathematical, three-dimensional, finite-difference, groundwater flow model of the Tesuque aquifer system in northern New Mexico was converted to run using the U.S. Geological Survey's modular groundwater flow code. Results from the final versions of the predevelopment and 1947 to 2080 transient simulations of the two models are compared. A correlation coefficient of 0.9905 was obtained for the match in block-by-block constanthead fluxes and 0.9845 was obtained for the match in block-by-block headdependent fluxes for predevelopment conditions. There are, however, significant differences in at least two specific cases. In the first case, a difference is associated with the net loss from the Pojoaque River and its tributaries to the aquifer. The net loss by the river is given as 1.134 cubic feet per second using the original groundwater model, which is 38.1 percent less than the net loss by the river of 1.8319 cubic feet per second computed by the new model in this study. In the second case, the large difference is computed for the transient decline in the hydraulic head of a model block near Tesuque Pueblo. The hydraulic-head decline by 2080 is, using the original model, 249 feet, which is 14.7 percent less than the hydraulic head of 292 feet computed by this study. In general, the differences between the two sets of results are not large enough to lead to different.conclusions regarding the behavior of the system at steady state or when pumped.