The influence of localization, posteruptive age and ethane-1-hydroxy-1.1 diphosphonate (EHDP) on artificial caries and its remineralization have been studied in human premolars. The depth of the lesions did not depend on the posteruptive age of the teeth, but on the localization on the teeth, presumably as a result of differences in morphological structure. At 30 μm from the surface of the enamel, an indication for a higher birefringence exists at a posteruptive age of 1 year than later on, suggesting a significantly higher de-mineralization which can be more fully remineralized, leading, in turn, to a lower birefringence. EHDP seems to stimulate, rather than to inhibit remineralization of artificial caries lesions in premolars with a posteruptive age of 1–5 yea