Topical F–– solutions, NaF, SnF2, TiF4, or Fe-Al-NaF, were applied to root surfaces to examine the effect on caries-like lesions produced in vitro. Extracted premolars were treated with a solution for 10 min prior to a 20-day period in acid gel. The lesions were studied by microradiography and light microscopy, and concentration profiles of 12 elements were determined by secondary ion mass spectrometry. The results indicated that the solutions retarded the development of lesions. The greatest effect was obtained with TiF4 and SnF2 solutions. Element analyses revealed that high concentrations of F (up to 3.5%) accumulated in the outer third of the lesion and that SnF2 and TiF4 formed depots in the cementum, although both Sn and Ti also penetrated the lesion. NaF had a weaker effect on lesion formation, but induced a high F concentration in the demineralized zones. The Fe-Al-F solution affected the lesion only marginally and deposited a relatively low F concentration in the lesion, although Fe and Al penetration and depot formation were noted.