The aim of the present study was to evaluate the effects of fluoride on erosive mineral loss in human enamel and dentine using a cyclic de- and remineralisation model in situ. The study was a three-treatment (5 days each) crossover design involving 4 (enamel) or 6 (dentine) healthy volunteers. Samples were recessed in palatal mouth appliances and worn day and night except during meals and were demineralised extraorally with 0.05 M citric acid (pH 2.3) for 6 × 5 min daily. Fluoridation was performed with toothpaste (SnF₂/Olaflur; 0.14% F^–) for 3 × 5 min daily (toothpaste fluoridation) or with toothpaste in combination with a mouthrinse (SnF₂/Olaflur; 0.025% F^–) for 3 × 5 min daily and with a gel (NaF/Olaflur, 1.25% F^–) on days 1 and 3 instead of the toothpaste (intensive fluoridation). In the control group no fluoridation was performed. Mineral loss (µm) was determined with the use of longitudinal microradiography. In enamel, mineral loss was 40.7 ± 15.1 µm in the control group, 18.3 ± 12.4 µm after toothpaste fluoridation and 5.0 ± 12.2 µm after intensive fluoridation. The respective values for dentine were 49.0 ± 15.4, 35.0 ± 15.5 and 19.8 ± 12.0 µm. All differences were statistically significant (p ≤ 0.001). The results indicate that intensive fluoridation is effective in preventing enamel and dentine from mineral loss even under severely erosive conditions.