The ontogeny of the behavioral ability to compensate for sodium deficit was studied in the rat. The experiments showed that: 1) Before weaning age, sodium-depleted pups will increase their avidity for 3% NaCl solution; 2) the ability to select and drink a salt solution in response to a sodium deficit continues to evolve between 17-24 days of age, and that pups at these ages will modify their intake of salt and water as do adult rats when rectifying plasma osmolality; 3) The increased appetite for sodium is evident even when depleted preweanlings are dehydrated and provided with solid NaCl tablets to lick, showing that sodium appetite and hydrational status are already dissociated at this age; and finally, 4) sodium depletion first induces an increase in intake of orally infused 3% NaCl solution in 12-day-old pups. The picture of the development of salt appetite in the suckling rat that these findings present is of a precocious competence to meet a challenge to sodium homeostasis. In this respect salt appetite emerges in parallel to the other ingestive behaviors.