Fluoride concentrations in the surface enamel of extracted incisors of adults were determined by prompt activation by proton bombardment. The teeth were then submitted to 4 min of topical fluoride treatments (commercial gels and solutions), and fluoride enrichments were measured after a short rinsing. The non-destructivity of the technique allowed to use the same area of the tooth before and after treatment. The highest amounts of fluoride were deposited in enamel treated with an amine fluoride solution (10,545 ppm). Good results were obtained with APF gels (2,200 ppm), whereas MFP gel gave a very low enrichment (243 ppm). Kinetic studies allowed to follow the rate of fluoride fixation which appears to vary according to a logarithmic scale.