This in vitro study aimed at evaluating the efficacy of a CO2 laser (10.6 mu m) alone or combined with acidulated phosphate fluoride (APF) on the inhibition of lesion progression in primary enamel. The specimens were treated with/without CO2 laser and/or APF and submitted to pH cycling. Microhardness analysis was performed and the enamel mineral loss values were obtained. The groups treated with laser and/or APF presented lower mineral loss when compared to the control group (p < 0.05). Laser irradiation alone or combined with APF decreased lesion progression in primary enamel. However, the combined treatment did not show any significant additional effect. Copyright (c) 2007 S. Karger AG, Basel.4117476