The influence of the original mineral content on the effect of one and two periods of acid attack was studied using quantitative microradiography. The maximum mineral content and the thickness of the surface layer, the minimum mineral content and the depth of the lesion were depicted as a function of the original mineral content. A linear relationship was found in all cases except in those groups with the highest original mineral content, where a flattening of the curve was seen. It may be concluded from the correlation between the lesion depth and the thickness of the surface layer that, when more material is dissolved in the lesion, more precipitation can take place near the intact surface, thus increasing the thickness of the surface layer.