The addition of tin to mouth rinses is, at least in vitro, a promising strategy for symptomatic therapy of dental erosion. The aim of this study was to evaluate the in situ efficacy of an experimental tin-containing fluoride solution on erosive tissue loss in human enamel and dentine. The study was a three-cell (7 days each) crossover design involving eight healthy participants. Samples were mounted on buccal shields of mandibular mouth appliances, which were worn for 24 h except during meals and drinks. Specimens were demineralised extraorally with 0.05 M citric acid (pH 2.3) for 6 × 5 min daily and were treated with test solutions intraorally once per day for 30 s after the first demineralisation. Three solutions were used: placebo (negative control), a commercially available tin- and fluoride-containing (SnF(2)) mouth rinse (positive control, 409 ppm Sn(2+), 250 ppm F(-), pH 4.2) and an experimental solution (pH 4.5) containing 1,900 ppm Sn(2+) (SnCl(2)) and 1,000 ppm F(-) (AmF/NaF). Tissue loss (micrometre) was determined profilometrically. In enamel, tissue loss was 54.8 ± 8.6 in the placebo, 24.5 ± 14.4 in the positive control and 9.7 ± 4.1 in the experimental solution group. The respective values for dentine were 48.5 ± 13.0 in the placebo, 32.8 ± 9.6 in the positive control and 26.2 ± 6.7 in the experimental solution group. The experimental solution was notably effective for enamel but was less effective for dentine. The positive control solution was less effective than the experimental solution; its effects for enamel and dentine were similar.