The effects of hemolymph sugar levels and carbohydrate metabolism on postfeeding diuresis in corn earworm moths, Helicoverpa zea (Boddie) were examined. High levels of ingested sucrose or the ingestion of nonmetabolizable sugars resulted in a reduced rate of diuresis. The magnitude of postfeeding diuresis appears to be dependent on the ability of the moth to metabolize ingested sugar after it has been passed to the hemolymph. Glycogen synthase (GS) and trehalose-6-phosphate synthase (TS) can reverse the increase in hemolymph osmolarity that accompanies sucrose digestion by the conversion of glucose to glycogen and trehalose. The level of fat body GS/TS activity correlates with differences in postfeeding diuresis between males and females and with changes in the magnitude of diuresis as moths age. These data suggest that the magnitude of postfeeding diuresis may ultimately depend on the enzymatic activities that control hemolymph sugar levels.