A scanning electron microscopic (SEM) study of the enamel surface layer of human natural white and brown spot lesions has been conducted in deciduous as well as permanent teeth. No ultrastructural difference was noted between white and brown lesions, and the brown spots were bleached after treatment in sodium hypochlorite. Observations of non-acid-etched surfaces of the carious lesions revealed (1) areas of apparently intact enamel, (2) focal holes, (3) a prismatic pattern of destruction and (4) an irregular type of destruction. SEM observations of non-cavitated incipient caries sections in depth showed enlarged prism sheaths in the intact surface layer which are definite pathways from the enamel surface to the body of the lesion. The concept of an intact enamel surface layer has to be reconsidered.