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To evaluate the influence of various light sources on the microhardness of human dental enamel following treatment with an in-office vital bleaching agent (35% hydrogen peroxide).One-hundred and sixty dental enamel slabs (-2.5 x 2.5 x 1.0 mm) were obtained from 32 recently extracted human third molars, polished and subjected to hardness testing (KHN, 50g-load, 5 seconds) after four time periods (baseline and after 1, 7 and 14 days). The specimens were placed in intraoral appliances and delivered to eight volunteers after being equally divided into five groups each according to the light source treatment to be performed extraorally (n=32): Group LA (35% hydrogen peroxide + argon laser unit); Group HA (35% hydrogen peroxide + halogen light-curing unit); Group LED (35% hydrogen peroxide + LED-laser unit); Group OX (35% hydrogen peroxide + no light source unit); or Group CO (control: saliva only). Microhardness values were analyzed by ANOVA and Tukey's post-hoc test (alpha = 0.05).Significant decreases in KHN were found in enamel for the HA group one day and seven days after treatment (5.81% and 2.35%, respectively) (p0.0001). However, no significant differences were found between the baseline and final microhardness values for all groups submitted to bleaching.The different tested light sources did not significantly influence the microhardness of human enamel following treatment with 35% hydrogen peroxide.