The ability of glass-ionomer dental cements to take up fluoride from a fluoridated mouthwash has been determined, and shown to vary somewhat with the degree of maturation (ageing). Three commercial conventional glass-ionomer cements were used to produce sets of five discs (6 mm diameter by 2 mm thickness). Discs were aged for 24 h or 1 month at 37°C then placed in 5 cm 3 volumes of commercial fluoridated mouthwash (Plax, ex Colgate Palmolive, Guildford, UK) at a nominal concentration of 112 ppm. Free fluoride ion concentration was measured in samples stored at room temperature for 30 min, 1, 2, 3, 4 and 5 h, using an ion selective electrode. Under these conditions cements were found to take up similar amounts of fluoride at t = 30 minutes, regardless of their age. However, at 5 hours the cements samples matured for 24 hours took up significantly more fluoride than the samples matured for 1 month. In this way it was shown that degree of maturation influenced the ability to take up fluoride without affecting the initial uptake rate. These results suggest that fluoridated mouthwashes may be a valuable source of fluoride for recharging glass-ionomer cements.