A comparison of the histology of enamel caries as observed by the optical microscope and the scanning electron microscope is reported. Preferential demineralisation of the prism cores commencing at their necks and involving ultimately the entire core is demonstrated. In addition to the prism sheaths it is observed that the striae of Retzius may also sometimes show resistance to demineralisation. From a comparison of the zones of enamel caries as observed optically with the SEM results it seems likely that some remineralisation occurs in the dark zone. In relation to the role of the organic matrix in the dissolution of the enamel, however, no assessment is possible since, at the present time, this matrix cannot be observed in the SEM.