The recent modeling technique to lactate (La) kinetics in exercise, and its availability, application, and limitation were summarized. Two examples were come up for discussion. One is the application of the compartment model (i.e., the description by the linear differential equations) to systemic La kinetics in exercise, and the other is the current controversy on anaerobic threshold, that is, the reexamination of the several proposed models of blood La kinetics during ramp exercise. In conclusion, considering the various limitations in current in vivo experimental approach on man, the theoretical approach with mathematical modeling, as one of the major strategies, gives full play to clarify the La metabolism in exercise.