Objectives: To compare the Ca2+ loss of enamel treated with 38% hydrogen peroxide (HP), 35% HP with light, and 10% carbamide peroxide (CP). Method and Materials: Ten extracted premolars were sectioned buccolingually and longitudinally so that 4 specimens were obtained from each tooth. The specimens were randomly assigned to 1 of 4 groups to receive the following bleaching agents: 38% HP, 35% HP with light, 10% CP, and no agent (control). The specimens were treated with an artificial caries solution (pH 4) for 16 days; the solution was replaced on days 4, 8, 12, and 16. Calcium concentration was determined by an atomic absorption spectrophotometer. Repeated measures ANOVA was performed on concentrations on days 4, 8, 12, and 16. Results: At the end of day 16, calcium ions released per square millimeter were calculated cumulatively as follows: 38% HP group: 27.52 +/- 5.22 mu g/mL; 35% HIP with light group: 25.15 +/- 4.99 mu g/mL; 10% CP group: 19.53 +/- 4.03 mu g/mL; control group: 18.35 +/- 4.00 mu g/mL. The differences between the control group and the 35% HP with light group and between the control group and 38% HIP group were statistically significant. Although demineralization differences were observed between the control group and the 10% CP group, this difference was not significant. Conclusions: It can be concluded that 35% HP with light and 38% HP may cause significantly more loss of Ca2+ from the enamel surfaces than 10% CP. Also, 10% CP does not vary significantly from the control.