This paper develops briefly four examples illustrating the use of crustaceans as experimental animals in the field of metabolic and transport physiology. In cells of euryhaline crabs, organic substances such as free amino acids contribute much more than inorganic ions to osmotic adaptation, a feature that is now realized to be of general importance in living organisms. Anhydrobiotic and anaerobically dormant embryos of the brine shrimp Artemia provide very convenient models to study cellular control of metabolic depression. Studies on amphibious crabs have highlighted the constraints imposed upon gas exchange and acid-base balance by the very contrasted properties of oxygen and carbon dioxide in water and in air. Finally, the blood oxygen transport system of decapod crustaceans has been a model of choice to demonstrate the significance of an increased oxygen affinity for adaptation to environmental hypoxia. These examples illustrate the role played in the past as well as the great future potential of crustaceans as experimental animal models for general studies in Comparative Physiology.