AIM: To compare the effects of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) paste and 8% arginine paste on dentin permeability. METHODS: Sixteen human third molars were sectioned to remove the roots and expose occlusal dentin surfaces. The pulpal side was flattened to obtain 1 mm remaining dentin thickness. Each specimen was attached on a Perspex plate and connected to a dentin-permeability measuring apparatus. The specimens were divided into two groups according to the tested products. Dentin permeability was measured under a simulated pulpal pressure after: (a) etching with 37% phosphoric acid; (b) application of CPP-ACP or 8% arginine paste; and (c) acid challenge with 2.6 mmol/L lactic acid. Twelve specimens were prepared so that the treated dentin surfaces could be examined using a scanning electron microscope. RESULTS: Dentin permeability after the application of 8% arginine paste was significantly reduced and lower than that of CPP-ACP paste (P < 0.01). Acid challenge with lactic acid significantly increased dentin permeability in both experimental groups (P < 0.01). The dentin surface treated with 8% arginine paste was covered with particles, but they were removed by acid challenge. Most dentinal tubules were patent when the CPP-ACP paste was applied. CONCLUSIONS: The application of 8% arginine paste decreased dentin permeability, but CPP-ACP paste did not.