In this work the effects of lead toxicity on dental enamel formation were studied. Epidemiological data and animal studies show an association between lead exposure and higher caries prevalence, but the mechanism underlying this association is still unknown. Here we present data on enamel formation in rats exposed to lead for 70 days in the drinking water. Enamel matrix was used for protein analysis and dry weight determination, while mature enamel was used for microhardness testing. Enamel matrix was scraped from the teeth and analyzed by electrophoresis in bulk or according to developing stage. Increased amounts of protein were observed in animals exposed to lead when the same weight of matrix was electrophoresed by protein electrophoresis. When extracts were prepared according to developing stages, no differences in the amount of protein or band pattern were observed. Upper incisors were cut longitudinally for Knoop enamel microhardness determination in four regions of the teeth. Microhardness analysis revealed statistically significant (P<0.05) decrease in the microhardness values of enamel from rats exposed to lead in regions of maturation but not of fully mature enamel. These results indicate a delay in enamel mineralization in incisor teeth from animals exposed to lead, highlighting a potentially important effect of lead toxicity not yet explored.