To clarify the hypophagic action of D-glucose, meal size, postprandial intermeal interval and eating rate were analyzed after infusion of glucose into the third cerebroventricle. The effects of glucose structure modification on feeding modulation were examined by comparing the effects of glucose to those of its epimers, D-mannose, D-allose and D-galactose. Glucose, infused in doses of 6 to 24 mumol, dose relatedly reduced meal size, but did not change other meal parameters. The minimum dose of glucose to induce feeding suppression was between three and 6 mumol. The epimers, at doses of 24 mumol, did not affect food intake or body weight. Drinking patterns and ambulatory activity were not changed by glucose infusion. These findings were consistent with neuronal activity observed in the ventromedial hypothalamic nucleus.