This paper describes a prototype interactive design tool, PSROUTE, that can be used by designers of data communication networks for selecting primary and secondary routes for every pair of communicating nodes in a network. The objective in selecting routes is to minimize the mean delay faced by messages. The problem was previously modeled as a mathematical programming problem (Pirkul and Narasimhan 1987). PSROUTE allows the user to interactively specify various network and traffic parameters and observe the effects on the solution. The solution can be examined in detail so that the designer can modify the parameters based on his judgment and then use PSROUTE to repeatedly execute the solution procedure until a satisfactory solution is reached.