The efficiency of a wheat:soy mixture (85:15 ratio) with and without supplementation of the limitant amino acids (methionine and lysine), was evaluated for: a. Supporting the normal rat growth previously fed with a casein diet (control group). b. The rat recovering with early and later protein-calorie malnutrition, and c. The animals ability (control and malnourished groups) in the self-selection for the limitant amino acids given. It was shown that the test diet, with and without supplementation, was adequate to sustain a normal body nitrogen content increase of the control groups animals. The principal changes in rat weight of the experimental animals during the recovering period were dependent on the nutritional state and the quantity of both, diet and amino acids intakes. As the age of rats increased, the diet intake (expressed as g of diet intake/100 g of rat) decreased in all experimental groups; this effect being more noticeable in malnourished groups. The self-selected intake of lysine and methionine, depends on: the previous nutritional state and the period of undernutrition of the animals; higher intake than the standard required values (Rogers and Harper) was observed in the three experimental groups. It was shown that the amount of methionine (gr met intake/100 g of wheat mixture) was directly related to lysine intake, expressed in similar units; significant correlation was observed: r = 0.816 (control group) and r = 0.789 (later malnutrition group) and highly significative r = 0.996 (early malnutrition group). The increase of the ratio between total body nitrogen and its initial value, was significative in all the cases. However the effect was more pronounced when the results obtained with early-malnutrition group are analyzed. The experiments performed with later malnutrition groups revealed that the increase of body nitrogen content was higher for supplemented diets than for animals fed with no-supplemented mixtures (the observed difference was highly significative p < 0.01). The analysis of body lipid content showed that the relative increase was much more significative for early malnourished groups. However in all the cases the effect of amino acid supplementation is almost negligible.