Several studies have demonstrated the caries protective effect of lasers by strengthening enamel crystalline structure. However, the effect of laser on enamel diffusion (ED) remains unclear. Objectives: This study aimed to quantify the laser-induced alteration of diffusion coefficients (DC) in enamel using fluorescence recovery after photobleaching (FRAP). Methods: Eleven caries-free enamel sections were characterized morphologically using stereomicroscopy, polarized light microscopy and scanning electron microscopy, before and after laser treatment with Er:YAG laser 50 mJ x 5 s x 5 Hz. With 20 mu M fluorescein, DCs were measured (n = 11) by FRAP coupled with confocal microscopy. Results: The DCs measured were 2.89 +/- 0.61 x 10(-7) cm(2)/s and 4.076 +/- 0.73 x 10(-7) cm(2)/s, at the lased and unlased areas, respectively (p = 0.001). Conclusions: This study has confirmed the reduction of ED as a potential mechanism involved in laser-induced caries prevention. FRAP was demonstrated to be a promising technique for evaluating diffusion-related phenomenon in enamel. (C) 2007 Published by Elsevier Ltd.