The effect of remineralizing and conventional toothpaste treatments on the hardness of intact and acid soft drink-etched enamel were assessed in a laboratory study. The remineralizing toothpaste (Enamelon Toothpaste) used in the study contains NaF, and simultaneously provides dissolved calcium, phosphate and fluoride ions. The conventional toothpaste contains NaF in a silica base. Sound extracted maxillary human incisors, mounted in epoxy resin with the facial incisal two-thirds exposed, were polished with 0.3 mu alumina. Groups of ten teeth were exposed to either twenty 5-minute treatments with an acid soft drink (pH 2.4), remineralizing or conventional fluoride toothpaste, or to twenty alternating cycles of a 5-minute protective treatment with either the remineralizing or conventional toothpastes, followed by 5-minute exposures to the acid soft drink, or to 20 five-minute exposures to the acid soft drink followed by 20 five-minute restorative treatments with the remineralizing or conventional toothpastes. Knoop Hardness measurements were made before and after treatment using a 500 g load and 15-second dwell time. Acid soft drink exposure produced a 15.4% drop in hardness compared with 4.9% and 1.6% hardness increases due to treatments of intact enamel with the remineralizing and conventional toothpastes, respectively. Protective treatments using the remineralizing and conventional toothpastes significantly reduced the drop in hardness due to acid soft drink exposure to 3.3% and 6.2%, respectively. Restorative treatments by the remineralizing and conventional toothpastes significantly increased the hardness of the acid soft drink-weakened enamel by 12.1% and 7.3%, respectively. Both toothpastes were effective in inhibiting damage due to acid soft drink exposure, but the remineralizing toothpaste was more effective in hardening intact and decalcified enamel than the conventional toothpaste (p < 0.05).