A complete model of the cholesterol system was developed in the rat. It synthesizes several partial models previously developed under different isotopic conditions. It contains 16 compartments and 40 parameters. It specifically describes the intestine (mucosa and contents), liver and plasma cholesterol subsystems. The model was validated by the similarity between the simulated and experimental values in all the compartments during the 48 hours following the single introduction of an isotopic label in two different parts of the system (single ingestion of 14C-cholesterol, intravenous injection of red cells containing 3H-cholesterol). The similarity between the simulations and the experimental values was also observed up to 4 months following labelled cholesterol ingestion as well as under other different isotopic conditions for shorter periods. The parameter values identified and the resulting fluxes agree with the already published data.