(1) The influence of various anions on activity of gustatory receptors was investigated by adapting the tongue of a frog to modified anion-Ringer, in which all Cl was substituted for Br, I, NO3, SCN, SO4 and H2PO4.(2) Immediately after exchange of normal Ringer with one of these modified anion-Ringers the response of the tongue was not appreciably changed in its threshold to various taste solutions and in its magnitude.(3) 1-2 hours after exchange of the bathing medium the response of the tongue to salt solutions was reduced and its threshold was raised, while the threshold concentration of sodium salts to depress water response was raised. The sensitivity of the tongue to other kinds of taste stimuli was not very much modified compared with that to salts.(4) Sooner or later all the sensitivities of the tongue to various taste stimuliwere reduced or abolished.(5) The effects of anions mentioned above depended on the anions used; the effectiveness was in the order of SCN>NO3>I>Br. Sulphate had no marked effects on gustatory receptors, while their response was readily abolished in phosphate Ringer.(6) The sensitivity of the tongue was rapidly restored when the phosphate Ringer immersing the tongue was replaced by normal Ringer, whereas the effect of other monovalent anions was irreversible.(7) The following hypothesis was presented on the mechanism of salt reception and of the depressing action of salts on water response: Entry of cations inside gustatory receptor from the exterior is the initial step for the initiation of salt receptor activity and withdrawal of the intracellular potassium ions may initiate water response, which is prevented by exsistence of a sufficient amount of cations permeable to the membrane outside the cell. Anions reduce the permeability of the membrane to cations in the order of SCN>NO3>I>Br> Cl, or alternatively the cellular potassium reduces in the presence of SCN, NO3, Ior Br.