Alterations in periodontal tissue were analyzed histologically in rats who had received a protein-deficient diet during intra-uterine life due to inadequate nutrition of the mothers and during the post-natal period due to the continuity of poor nutrition. The animals were weighed at sacrifice: 0, 1, 4, 11, 17, 21, 42, 50 and 105 days. Histological data comparing the undernourished and control groups will be the objective of a future publication. This first part reports the statistical analysis of weight progression of the two groups, concerning not only the mean weight, but also the individual weight of each animal at the various sacrifice periods. Weight progression was gradual and proportional in each group, despite the fact that the control group had accentuated weight gain, deviating, with time, from the weight of the undernourished group of the same age.