The release of fluoride from a composite resin has been shown to inhibit enamel demineralization. The purpose of this study was to examine the remineralization effects of a fluoride-releasing resin. Twenty extracted molars were painted with an acid-protective varnish, excluding a 2 x 6-mm window. Artificial carieslike lesions were created in the exposed enamel with an acidified gel. A Class II preparation was restored with a fluoride-releasing or a non-fluoride-releasing composite resin. The teeth were sectioned longitudinally and photographed with polarized light microscopy in water and Thoulet's imbibition media. The sections were then painted with an acid-protective varnish, so that only the natural external surface of the lesion was exposed, and placed in separate closed enivronments of a nonfluoridated artificial saliva. Sections were removed after 2 weeks and 3 months and photographed under polarized light as before. A sonic digitizer was used to measure the area of the body of the lesion. Results demonstrated a statistically significant area reduction in the body of the lesions exposed to the fluoridated composite resin at 2-week and 3-month intervals.