The present study examines early enamel surface alterations taking place when active carious lesions enter an arrested stage. Orthodontic bands with a standardized space for plaque accumulation were used to produce incipient carious lesions on the buccal surface of all four first premolars of four young adolescents. The premolars were to be extracted for orthodontic reasons. After 4 weeks of local cariogenic challenge, all teeth were debanded. In each patient one tooth was extracted at the time of debanding. The remaining premolars were extracted 1, 2, and 3 weeks after re-exposure to the oral environment. No fluoride was added during the entire test period, and the patients were told to maintain usual oral hygiene. Scanning electron microscope examination of the experimental surface areas disclosed a gradual wearing away of the outermost crystals during the 3 weeks of observation. This was associated with a leveling off of surface irregularities and the development of a multitude of scratches. The observed attrition of the porous surface in the lesion area indicates that functional wear and toothbrushing were responsible for the arrestment by disturbance and removal of bacterial deposits.