Effects of treating the tongue with 7 heavy metal salts on chorda tympani nerve responses to sweet, salty, sour, and bitter stimuli were studied in ddy mice. CuCl₂ and ZnCl₂ at 10^-5M inhibited responses to sucrose and Na saccharin without affecting responses to the other taste stimuli. Inhibition of responses to sweet stimuli was reversible, but recovery was very slow. No such selective inhibition of sweet responses was observed with FeSO₄, MnCl₂, CoCl₂, NiCl₂ or CdCl₂. FeSO₄ (1mM) had a very small effect on all responses. CdCl₂ (1mM) depressed responses to all the stimuli to some extent. MnCl₂, CoCl₂, and NiCl₂ (1mM) slightly inhibited responses to NaCl and quinine hydrochloride, but not HCl. Responses to sweet stimuli were slightly inhibited by 1mM MnCl₂ or CoCl₂. Kinetic analyses of the inhibition of sucrose responses by CuCl₂ indicate that it is a competitive inhibition. Based on the results it is hypothesized that Cu²⁺ and possibly Zn²⁺ also compete with sweet-tasting molecules for receptor proteins while other heavy metal ions do not possess a strong ability to bind to the proteins.