To evaluate the effect of protein-energy malnutrition (PEM) on the growth of the mandible and incisor teeth as well as to know if the malnutrition produces modifications in the time of the eruption of the teeth in malnourished rats during the lactation period, animals were divided into experimental and control groups. Experimental pups fed by one mother's milk were doubled in their number to be twice to those of the control pups fed by one mother's milk (Park method). The animals were sacrificed at 20 and 40 days of age, and the body and total lengths of the mandible, and the transverse and antero-posterior diameters of the incisor teeth were measured. The time of the eruption of the mandibular incisor teeth in both groups was also assessed. Data were statistically compared by Student's t-test. Experimental animals at both ages showed a significant reduction in the growth of the mandible and the mandibular incisor tooth in all parameters. A delay in the time of the dental eruption in malnourished rats was als o observed. The effect of PEM during the lactation period (newborn-20 days) not only appeared at the end of this period but it lasted up to the end of the postweaning period (21-40 days).