The beneficial effect of fluoride-containing amalgam in preventing recurrent dental caries depends on the ability of the material to deliver fluoride (F). A two-chamber diffusion cell has been employed to monitor the diffusion of F in freshly prepared amalgam sections (membranes) as well as in amalgam sections stored in F solution for 15 d. The diffusion of 125I was also monitored, as a reference. Five and ten successive measurements at 72 h intervals were made on the fresh and stored amalgam specimens, respectively. The average diffusion coefficient, D, of F and 125I in fresh amalgam was 2.39 x 10(-10) and 1.85 x 10(-10) cm2/s, respectively. For stored amalgam, the average D of F during a 30 d experiment was 1.35 x 10(-10) cm2/s. The average D of F in stored amalgam, during the first 15 d of the experiment, was 31% less than in fresh amalgam (p less than 0.01). A decline in the diffusion process was observed during the course of the experiments. During 15 d diffusion in fresh amalgam and 30 d diffusion in stored amalgam the cumulative diffused F were 0.79 and 0.88% of the F in the source. SEM findings revealed the deposition of corrosion products on amalgam stored for 3 months in 0.19% F solution.