This study examines imposing and testing restrictions on preference variables in the Rotterdam model through the impacts of these variables on marginal utilities. An empirical analysis of the impact of a female labor force participation variable in a Rotterdam demand system for fresh fruit illustrates the methodology. This variable was modeled through its impact on marginal utilities via "adjusted" prices, following theoretical work by Basmann and Barten, among others. Results show that the female labor participation has negatively impacted the demands for citrus, while positively impacting the demands for other fresh fruit.