The aims of this study were firstly to investigate the fluoride-releasing characteristics of five commercial glass ionomer materials: Ketac Fil, Chemfil Superior, Fuji II LC, Aquacem and Vitrebond. The second aim was to assess the fluoride uptake and subsequent release from the same range of materials. In both tests, ten discs, 6 mm in diameter with a thickness of 1.5 mm, were made for each material. The initial fluoride release was assessed over a 60-day period for all materials. Each disc was immersed in 2 ml of de-ionised water within a plastic vial. The solutions were changed daily up to day 15, and thereafter every 3 and 4 days until the end of the test. All of the materials released measurable amounts of fluoride throughout the test period, with a considerable range on day 1 (15.3–155.2 ppm F). The concentration of fluoride released on the 2nd day fell sharply for all materials (range 6.3–44.3 ppm F). By day 60 all materials continued to release fluoride, albeit to a lesser extent (range 0.9–3.99 ppm F). With regard to the uptake and release of fluoride, a similar protocol was employed, although all samples were immersed in 1 litre of de-ionised water for 60 days to allow the majority of the fluoride to leach out from the materials. The ten pellets for each material were divided into two groups, five samples as control and five samples as test. Each day over a 20-day period all test samples were exposed to a 1000-ppm F solution for 2 min. Fluoride uptake/release was assessed from the 2 ml of de-ionised water in which the samples had been immersed for 24 h. The control samples continued to release small concentrations of fluoride throughout the test. The test samples, exposed to the 1000-ppm F solution, consistently released more ionic fluoride than the controls at all time points from day 1 to day 20, indicating that fluoride had been taken up and subsequently released. The values ranged at day 1 from 3.29 ( ± 0.14) for Aquacem to 7.63 ( ± 0.13) for Ketac Fil at day 1, rising to values between 869 ( ± 1.88) for Aquacem to 10.34 ( ± 1.61) for Vitrebond at day 20. This study indicates that all five glass ionomer cements take up as well as release fluoride and that the amount of fluoride released may be of profound clinical significance.