A mathematical model of lactating sow metabolism was evaluated using three types of tests. First, 16 experimental treatments from four experiments reported in the literature were simulated with the model, and the simulated values for change in BW and protein and fat content were compared to reported or calculated values. Second, the model's response to level of feed intake, level of milk production, BW and composition at farrowing, and dietary lysine concentration was compared to expected responses. Third, the model's sensitivity to changes in several of its kinetic parameters was measured. There was good agreement between simulated and measured values for BW and fat loss and reasonable agreement for body protein loss. All responses to changes in external conditions were in expected directions and biologically reasonable. The model seemed rather robust with respect to changes in the kinetic parameters considered, although important changes in simulated values were found in some cases. Overall, the model seems sound. It can be useful in evaluation of feeding programs and in understanding biological relationships.