The gustatory responses from thechorda tympaninerve of the Mongolian gerbilMeriones unguiculatuswere tested with some methyl glycopyranosides and inhibitors. Except for one compound, methyl 4,6 dichloro-4,6-dideoxyα-D-galactopyranoside, all sugars stimulated the taste nerve. In our previous research, we found one of the most effective methyl glycosides was methylα-D-glycopyranoside (MAD-Glu). We also found that methyl glycosides, which differed from MAD-Glu by the orientation of a substituent group at C-1, C-2 and C-4, were always less effective taste stimuli. In our present study, we have extended this finding to include the C-3 epimer which was also found to be less effective than MAD-Glu. In a second set of experiments, we looked at deoxy sugars. In contrast to orientation effects found in the epimers, substitution of the hydroxyl groups of MAD-Glu by hydrogen atoms (deoxy-sugars) had variable effects. The 3-deoxy and 6-deoxy derivatives were found to be as effective as MAD-Glu, while the 4-deoxy derivative was less effective. In addition, substituting chlorine atoms for the hydroxyl groups appears to have a deleterious effect. For example, the 6-chloro derivative was less effective than MAD-Glu while the 4,6-dichloro derivative of methylα-D-galactopyranoside did not stimulate the nerve at all. Finally, in addition to structure-activity experiments mentioned above, we examined the possibility that the sugar taste response may involve other physiological factors. In this vein, we found that the sugar transport inhibitors phloretin and phlorhizin and the sodium channel blocker, amilonde had no effect on the gerbil's sucrose or glucose taste respon