A two equation model is developed to examine jointly the determinants of household food stamp program participation and program effects on food expenditures. The model is unique in that it postulates that the participation decision is based on a cost-benefit ratio, selected socioeconomic characteristics, and the potential for increasing both food and nonfood expenditures. Data from the 1977-78 USDA Nationwide Food Consumption Survey Supplemental Low Income Sample is used to estimate the model. Findings suggest that households, in making the participation decision place equal value on the potential for increasing their food and nonfood expenditures. However, at the margin, bonus stamp income is found to have more than twice the impact of money income on food expenditures. The model's potential for policy analysis is also examined.