In this investigation, the calcium content of sound decalcified and etched enamel was measured with an electron microprobe. The results show that calcium content, as a function of depth, decreases only a few percent as a result of decalcification in gelatin solutions of pH 4 and 5 within 1–8 days. Subsurface lesions (with a relatively low Ca concentration) could be observed. These lesions penetrated under the enamel surface at a rate proportional to the square root of the decalcification time. In etched enamel, however, the Ca decrease observed (also a few percent) was uniform over the whole penetrated area.