The aim of this study was to register the fluoride distribution in cavity walls following exposure to a fluoride-containing amalgam in vitro. Class V cavities were prepared on buccal and lingual surfaces in ten extracted premolars and filled with a fluoride-containing (experimental) or a conventional (control) amalgam. After storing the teeth in artificial saliva for three months, the fillings were removed and the cavity walls analyzed with an electron microprobe. The cavity walls which had been exposed to the conventional amalgam did not show F concentrations above the detection limit (0.15%). In the experiment group, however, more than 60% of the analyses of the enamel walls revealed fluoride concentrations greater than 0.15%, the values ranging from 0.2 to 1.7%. In the dentin walls fluoride concentrations of 0.2 - 1.9% were measured. However, 80% of the analyses revealed values between 0.9 and 1.5%. The depth of the zone of increased F concentration in enamel and dentin walls was on the average 27 and 108 micrometer, respectively. Although the concentrations should only be regarded as semiquantitative values, they indicate that considerable amounts of fluoride are deposited in the cavity walls from the fluoride-containing amalgam.