The use of permanent magnets in orthodontic treatment has increased significantly over the past years, triggered by the introduction of rare earth magnetic alloys. Concerns about possible side effects have been expressed relating to their use in orthodontic treatment. In previous experimental studies evidence of a reduction in bone formation and epithelial turnover close to rare earth magnets has been presented. The aim of the present study was twofold: to confirm earlier results and to study whether the observed changes are reversible. One hind leg in each of 45 rats was fitted with aluminum rings with Co5Sm magnets, whereas the other hind leg was fitted with sham rings. After 8 weeks 25 rats were killed, and the rings in the remaining rats were removed. The latter group was killed after another 11 weeks. The epithelial and bone reactions were evaluated histomorphometrically. Previous results showing thinner epithelium and retarded rate of bone formation close to Co5Sm magnets were confirmed. These effects were also shown to be largely reversible. It was concluded on the basis of this and the magnitude of the effects that any local side effects from orthodontic rare earth magnets appear negligible when extrapolated to the clinical situation.