OBJECTIVE To evaluate remineralization efficacy of an arginine containing dentifrice on initial enamel carious lesions in vitro. METHODS Human enamel blocks with early lesions were prepared and randomly divided into three treatment groups: negative control group (distilled and deionized water), positive control group (fluoride containing dentifrice and 0.14% sodium monofluorophosphate), and test dentifrice group (8.0% arginine and 0.14% sodium monofluorophosphate). The lesions were subjected to a pH-cycling regime for 10 days. Surface enamel microhardness of the enamel blocks from each group was measured before and after pH cycling, and the surface microhardness recovery was calculated. Then, specimens were analyzed for enamel fluoride uptake (EFU) through acid etching method, after which they were treated in demineralization solution for a 2 h period of acid challenge. The other specimens were sectioned and examined through polarized light microscopy. RESULTS In the test dentifrice group, microhardness recovery and EFU were significantly higher than those in the negative control and positive groups. The test dentifrice group was significantly resistant to the acid challenge compared with the other groups. Conspicuous remineralization of enamel subsurface lesions was observed under polarized light microscopy among samples treated with test dentifrice, whereas the control groups showed no significant changes on enamel subsurface lesions. CONCLUSIONS This study presents the potential superiority of Pro-Argin dentifrice over conventional fluoride dentifrice in promoting the remineralization of initial enamel lesions.