The aim of this study was to visualize fluid movement through dental enamel in vivo. Fifty permanent upper central incisors, from subjects aged 10-70 yr, and 5 permanent central just-erupted incisors, from subjects aged 6-7 yr, were included in the study. An impression was obtained by vinyl polyxiloxane, and replicas were then obtained by polyether impression material. The hydrophobic vinyl polyxiloxane material yielded a morphological image in situ of outward fluid flow through tooth enamel. The study confirmed in vivo that enamel is a permeable substrate, as shown by the presence of droplets on its surface, and demonstrated that age and enamel permeability are closely related. Samples from subjects of different ages showed a decreasing number and size of droplets with increasing age: freshly erupted permanent teeth showed many droplets covering the entire enamel surface. Droplets in permanent teeth were prominent along enamel perikymata.