This paper describes an interactive computer program which allows direct access to one version of the National Linear programming models on line at the Iowa State University computer. The user can enter changes in crop yields or production costs and obtain a solution to the revised model with a summary which can be printed at his remote terminal. The system lends itself to quick studies of the impact of exogenous changes in crop production possibilities, such as impacts of droughts, restraints on fertilizers or pesticides and the like.