The summated response from the chorda tympani proper nerve of 9 monkeys was recorded during stimulation with solutions of acetic and citric acids, sodium chloride, quinine sulfate, sucrose, glucose and fructose before and after application of extracts of Synsepalum dulcificum-miraculin- and Gymnema sylvestre-gymnemic acid-on the tongue. It was observed that (a) miraculin enhanced the response to all acids used (b) miraculin had no significant effect on the response of the other taste stimuli (c) its effect lasts for more than ½h and was not removed by rubbing of the tongue (d) gymnemic acid had no significant effect on the response to any of the stimuli used if miraculin had not been applied beforehand (e) gymnemic acid applied after miraculin diminished the response to acid, then miraculin enhanced the response to acid again. It was concluded that these electrophysiological findings in monkey parallel the psychophysical observations in man with regard to the effect of miraculin and gymnemic acid on the response to acids, but that they differ with regard to the effect of gymnemic acid on the response to sugars.