The potential risks of mercury dissolution from dental amalgam have long been recognized. This study examined the effect of hydrogen ion concentration on the release of mercury from two dental amalgams: an admixed high-copper amalgam and a new tin- and copper-free amalgam. Specimens of each type of amalgam were incubated in citric acid buffer o f pH 2.5 or pH 7.0. Results showed that, for both types of amalgam, specimens incubated at pH 2.5 released stati stically significantly greater (P .0001) quantities of mercury than did specimens incubated at pH 7.0. Release of mercury from the tin- and copper-free amalgam was also statistically significantly greater (P .0001) than that of the high-copper amalgam at both pH level