Remineralization of human enamel is an important issue in the prevention of caries. Fluoride has an important influence on the remineralization process. A great deal of research has been done into the role played by the method of application and by the concentration and type of fluoride. In the clinical study of this dissertation the process of remineralization of lesions in human enamel was longitudinally followed in vivo during a period of 3 months. Both the remineralization in the surface softened enamel lesion and the subsurface enamel lesion of human enamel were studied. In addition, attention was devoted especially to the influence of fluoride on this remineralization. The results indicated that the use of a 1,500 ppm fluoridated NaF toothpaste was more effective on the remineralization process than the use of a 50 pmm NaF mouthrinse. Important is the fluoride gradient in the enamel lesion, and in particular the fact that fluoride reaches the lesion front. This most likely accounts for the remineralization efficiency.