We conducted a sensitivity analysis using a numerical model of fractured porous media to find out how porous media and fracture parameters affect solute transport. The 2-dimensional, saturated fracture flow and transport code FRACTRAN was used to conduct the simulations. Seven parameters were considered: matrix hydraulic conductivity, matrix porosity, retardation of the matrix, gradient of the flow field, fracture retardation, fracture aperture, and fracture probability (which incorporates fracture spacing and fracture length). A Latin-hypercube design was used to select a matrix of parameter values that minimized correlations among the design parameters. The results were summarized by examining least square fit of the relationship between the seven parameters and 50% breakthrough time and spread of the breakthrough curves, with nearly identical results. The matrix parameters, in particular hydraulic conductivity and porosity, had the greatest effect. As expected, fracture probability was nearly equivalent in importance. These results indicate that field characterization in fractured porous media should not only emphasize fracture location, which strongly influences directions of contaminant transport, but also matrix properties, which have a major influence on contaminant residence times and breakthrough concentrations. ¿ American Geophysical Union 1995