Objectives: In this in vitro study, the authors sought to determine the effects of 1.23% acidulated phosphate fluoride gel (APF) or drinkable yogurt on human enamel after exposure to an acidic drink. Method and Materials: Sixteen surgically removed, caries-free, human third molars were cut into four portions: mesial, distal, buccal, and lingual. Each portion was distributed into one of four groups, with each specimen embedded in acrylic resin and its enamel center lightly ground and polished. Three groups of specimens were immersed in orange juice for 2 minutes. One group received no other treatment (OR), one group was subsequently immersed in drinkable yogurt for 5 minutes (OR:YO), while another group had 1.23% APF applied for 4 minutes (OR:APF). The final group was immersed in only drinkable yogurt for 5 minutes (YO). Each exposure was performed twice daily for 60 days; between exposures, the samples were stored in artificial saliva. The enamel surfaces were monitored by three criteria: erosion depth, surface hardness, and SEM. Results: Erosion depth increased progressively in all groups. Surface microhardness progressively decreased in all groups except the OR:APF group, where hardness was significantly higher than other groups at 60 days (P .05). SEM inspection revealed preferential loss of rod crystallites with retention of interrod crystallites in all specimens exposed to orange juice. The enamel exposed to only drinkable yogurt revealed modest and uniform etching. Conclusion: Drinkable yogurt alone or posttreatment of enamel after exposure to an acidic drink with either 1.23% APF or drinkable yogurt leads to enamel dissolution and does not reduce enamel erosion, in vitro. Keywords: 1.23% acidulated phosphate fluoride gel, drinkable yogurt, enamel erosion, in vitro