Behavioral and electrophysiological experiments with 10 sweeteners have been made to test if gymnemic acid (GA) is able to block the response to sweet stimuli in single taste fibres of the chorda tympani proper nerve in hamsters. The hamster was chosen because earlier studies show that it is more sensitive to GA than any other non-human species. Since GA has been shown to affect the sweetness of many different substances, its effects were studied on an array of sweeteners. To avoid, however, the inclusion of sweeteners unpalatable to the hamster, the hamsters' liking of this array was tested with two-bottle preference technique for -24 h. It was found that acesulfam-K, fructose, glucose, sucrose and xylitol were strongly liked, while the animals showed no preference for aspartame, D-tryptophane, sodium cyclamate, sodium saccharin and thaumatin over water. The summated nerve response of these stimuli was then recorded. It was found that neither thaumatin nor aspartame elicited a response, while the other stimuli gave a good response. Finally, the sweeteners which were both preferred in the two-bottle tests and gave a nerve response were used as taste stimuli in single fibre experiments together with sodium chloride, quinine hydrochloride, citric acid and saccharin. The single fibre recordings were made before and after application of 5 mg GA for 3 min on the tongue. It was found that GA did not cause any dramatic decrease or disappearance of the responses to either the sweet or the non-sweet substances. The responses to the sweeteners, however, were more depressed than those to the non-sweet stimuli.