Gustatory afferent activity and the perceptions it evokes have proven to be modifiable by physiological needs. We monitored changes in taste responses in the rat nucleus tractus solitarius (NTS) as a function of blood glucose levels. Taste stimuli were 0.1 M NaCl, 1.0 M glucose, 0.03 M HCl and 0.01 M QHCl. Gustatory activity was selectively modified as an inverse function of blood glucose. Intravenous injections caused blood glucose levels to rise from 90 to near 200 mg% 5-15 min post-injection, with slow recovery thereafter. During the 5-15 min period, NTS responses to glucose were depressed an average 43%, NaCl by 20%, HCl by 16% and QHCl by 3%. Time courses of all responses were unmodified. This effect, probably mediated either by glucoreceptors in NTS or by vagal afferents from the gut, suggests a particular suppression of more appetitive tastes, and so may provide a neural concomitant to the decreased appeal of food which accompanies satiety.