A physiologically based pharmacokinetic model for exposure to inorganic arsenic in hamsters and rabbits has been developed. The model in its present state simulates three routes of exposure to inorganic arsenic: oral intake, intravenous injection, and intratracheal instillation. It describes the tissue concentrations and the urinary and fecal excretions of the four arsenic metabolites: inorganic As(III) and As(V), methylarsonic acid, and dimethylarsinic acid. The model consists of five tissue compartments, chosen according to arsenic affinities: liver, kidneys, lungs, skin, and others. The model is based on physiological parameters, which were scaled according to body weight. When physiological parameters were not available, the data for the model were obtained by fitting (tissue affinity, absorption rate, and metabolic rate constants). The excretions of the arsenic metabolites in urine and feces are well simulated with the model for both species. Further validation of the arsenic metabolite concentrations in the tissues and in vitro measurements of the tissue affinity constants are discussed.