Salivary fluoride concentrations were determined in 10 children (mean age 12.0 years) undergoing fixed orthodontic therapy. The orthodontic appliances, a minimum of 4 bands and 8 brackets, were cemented with a glass ionomer cement. Unstimulated whole saliva was collected 4 times a day before (baseline value) and at 1, 7, 14 and 28 days after cementation. The samples of saliva were centrifuged and the supernatants were analyzed with a fluoride-sensitive electrode. At baseline, the mean salivary fluoride concentration was 0.85 mumol/l. There was a significant increase during the day after cementation (1.88 mumol/l). After 7, 14 and 28 days, salivary fluoride levels were slightly elevated, but not statistically different from the baseline values. The ingested fluoride dose during the 1st day was estimated to be 0.02 mg. It is concluded that in orthodontic treatment with fixed appliances, a slow release of fluoride from glass ionomer cements could exert a local cariostatic effect on adjacent caries-susceptible enamel.